The South China Sea in 2025: Dead Calm or Surging Undertow?

 

The South China Sea continues to witness diverse forms of cooperation, with stakeholders engaging in efforts to manage the situation. In the first ten months of 2025, cooperative initiatives and efforts emerged in a variety of domains to promote stability.

 

 

Cooperation was visible through both bilateral and regional diplomacy, whose substance touch upon maritime domain in general or the South China Sea in particular.

 

From China’s side, China has been promoting South China Sea cooperation, or maritime cooperation with Southeast Asian nations via a series of high-level engagements. Most notably, in March 2025, during his visits to Vietnam, Malaysia, and Cambodia, Chinese President Xi Jinping highlighted practical collaboration in less sensitive maritime issues with Vietnam,¹ expanded the prospect for joint marine science and technology research with Malaysia,² and reiterated with Cambodia that the South China Sea disputes should be resolved peacefully by directly concerned parties.³

 

From Southeast Asia side, the favor seems to have been returned at a certain level via several cooperation commitments. In January, China and the Philippines convened the 10th meeting of the Bilateral Consultation Mechanism on the South China Sea, agreeing to enhance dialogue and promote cooperation in areas such as coast guard affairs, science and technology, and marine environmental protection⁴. In February, China and Brunei signed a joint statement committing to cooperate in resource development in the South China Sea.⁵ In May, during Chinese Premier Li Qiang’s visit to Indonesia, the Indonesian President Prabowo declared readiness to cooperate with  China in implementing agreements on joint maritime development.⁶

 

In August 2025, China and ASEAN also reached Plan of Action to implement the ASEAN-China Comprehensive Strategic Partnership (2026-2030), emphasizing commitment to the full and effective implementation of the Declaration on the Conduct of Parties in the South China Sea (DOC) and progress towards the early conclusion of an effective and substantive Code of Conduct in the South China Sea (COC), that is in accordance with international law, including the 1982 United  Nations Convention on the Law of the Sea (UNCLOS).⁷

 

The 47th ASEAN Summit and related Summits in Malaysia (October 26-28, 2025) also witnessed a number of notable meetings and outcomes that bear implications for the South China Sea and rule of law. Thailand and Cambodia signed a peace deal, with the oversight of Malaysian Prime Minister Anwar Ibrahim and U.S. President Donald Trump⁸. ASEAN-U.S. Leaders’ and ASEAN-Japan’s joint statements emphasized the importance of UNCLOS, with U.S. President Donald Trump reaffirming U.S. commitment to ASEAN and regional security.⁹ Chinese Premier Li Qiang held trade talks with the U.S. delegation and a meeting with Australian Prime Minister Anthony Albanese. 

 

From the U.S. side, the Trump 2.0 Administration has gradually affirmed its commitment to the regional maritime security. After nine months in office with barely any direct reference of the South China Sea, the Trump 2.0 Administration issued the first-of-its-kind factsheet¹¹ on U.S. commitment to maritime security in the Indo-Pacific region, including the South China Sea, expressing its deep economic and security interests in regional maritime security, with special focus on maritime domain awareness, law enforcement, maritime operations and diplomatic engagement. This was also their message at the ASEAN Summit in October 2025, and was followed up with concrete programs such as the U.S.-led P140 maritime security initiative for the Philippines, launched on Oct 17. Straining over three years, this initiative will include intensive training courses to improve the operational capacity of the Philippine Coast Guard.¹²

 

 

Key stakeholders maintain their military presence in the South China Sea via a series of exercises in the first 10 months of 2025.

 

From China’s side, the PLA  Navy dispatched the missile frigate Xuchang and the minesweeper Xichui to participate in the joint maritime exercise China–Singapore Cooperation 2025 at Singapore’s Changi Naval Base from May 9 – 16.¹³

 

From ASEAN’s side, Southeast Asian states participated in at least 49 joint maritime exercises and patrols, surpassing the total number recorded in 2024 (48 exercise).¹⁴

 

 

Middle powers organized or joined at least 35 bilateral or multilateral regional exercises, including 17 in the South China Sea, slightly fewer than total 19 of 2024, but still maintaining the common trajectory.¹⁵

 

Maritime Cooperative Activities (MCA), primarily involving the Philippines, the U.S., and six other U.S. allies/partners (including Japan, Australia, Canada, France, New Zealand, and India), have become increasingly prominent in the South China Sea. Since their inception in November 2023, 22 MCA have been conducted including 12 bilateral and 10 multilateral activities. Of these, 12 MCA took place in 2025 alone, consisting of seven bilateral exercises—two conducted without U.S. participation—and five multilateral engagements.

 

Also worth noting, Balikatan 2025, the annual US-Philippines exercise marked the largest in history, involving 14,000 troops. The drills highlighted enhanced multilateralism with the participation - both formal and observers - of middle powers including Japan, South Korea, Australia, the United Kingdom, France, Germany, India, the Netherlands, and New Zealand.¹⁷

 

 

The legal front often receives less attention than the flashy on-the-ground developments, but this is where actions can bear direct implication on the “rule of law” in the South China Sea.

 

The cooperation here can be seen mostly via ASEAN and China’s negotiation efforts for a COC. As ASEAN Chair in 2025, Malaysia placed top priority on accelerating COC negotiations in order to achieve an “effective and substantive” framework to manage tensions in the South China Sea. The Philippine Foreign Minister noted that China had made a “political commitment” to conclude the COC before 2026. The Philippine President, at the 46th ASEAN Summit, called on ASEAN to urgently adopt a legally binding COC. Additionally, Indonesia is set to ratify its exclusive economic zone (EEZ) delimitation agreement with Vietnam, as announced by President Prabowo Subianto during the visit of the Communist Party of Vietnam Secretary General To Lam to Jakarta on March 10.

 

Many countries also coordinated in their signaling on the eve of th Anniversary of the Philippines-China South China Sea Arbitral Tribunal Ruling. 15 countries and the EU (as an international organization) issued statements in support of the Award, at different levels and on different platforms. Notably, Slovenia voiced support for the Award for the first time this year, raising the total number of countries supporting the Award to 28.

 

The number of countries joining the Agreement on the Conservation and Sustainable Use of Marine Biological Diversity of Areas beyond National Jurisdiction (BBNJ) also increased, with 145 signatories and 75 parties. The BBNJ is related to the South China Sea as there might exists a small pocket of international waters in this water, indicating a possibility of an MPA establishment in accordance with BBNJ. Vietnam was among the first nations to sign the BBNJ on the opening day in 2023 and swiftly completed its domestic procedures to become an official party, with reservation and interpretative declaration on June 9, 2025).¹⁸

 

 

Despite repeated cooperation efforts, the South China Sea remains an area of contestations and associated risks. The first 10 months of 2025 have underscored its persistent volatility, with underlying frictions emerging across multiple domains, from maritime operations and political maneuvering to legal contestation, narrative competition, and economic rivalry.

 

 

The contestation can be observered most visibly via stakeholders’ on the ground deployment. China and the U.S. are the key player in this domain, with their series of military exercises or “gray-zone” deployments, in or around the South China Sea. Other middle powers, who usually tread the “competition” line carefully, have also been more active in military deployment.

 

China and the Philippines experienced at least ten incidents at Second Thomas Shoal, Scarborough Shoal, Sabina Shoal, Sandy Cay, and surrounding areas. According to the Philippines, China has increasingly deployed multiple forces to maintain presence in Philippine waters. China Coast Guard (CCG) vessels 5901 and 3103 maintained a long-term presence within the Exclusive Economic Zones (EEZs) of the Philippines, Malaysia, and Vietnam. The CCG landed personnel and raised a flag on Sandy Cay,¹⁹ and for the first time used water cannons against Philippine vessels near the reef.²⁰ Notably, a CCG ship collided with a Chinese Navy ship while attempting to chase a Philippine patrol boat in waters near Scarborough Shoal in August 2025, reportedly causing severe damage to the CCG ship.²¹

 

Tensions also simmer between China and other middle powers in the South China Sea. There were at least two mid-air incidents between China and Australia in the South China Sea on February 11 and October 19, in which China reportedly released flares in close proximity to the Australian patrol aircrafts and both sides traded accusations.

 

Unilaterally, China conducted at least 131 drills, live-fire exercises, military training, and naval deployments in the South China Sea and the Gulf of Tonkin, surpassing the total numbers in three previous years (119 in 2024, 86 in 2023, and 96 in 2022).²²

 

The U.S. reportedly conducted two Freedom of Navigation Operations (FONOP) in the South China Sea on 12 May near the Spratlys Islands and on August 13 near Scaborough Shoal (the first FONOP at Scarborough  Shoal since 2019). The U.S. deployed aircraft - more than in the latter half of 2024 (once), but fewer than the first half of 2024 (three times).

 

In the region, the U.S. carried out at least 97 joint exercises/patrols, surpassing the total 91 of 2024.²³ Of these, 24 took place in the South China Sea. The remainder occurred in U.S. territories in the Pacific, as well as in allied and partner territories, international waters, or geopolitical “chokepoints” such as the Strait of Malacca and the East China Sea. The U.S. deployed the NMESIS anti-ship missile system to the Philippines and, for the first time, and stationed B-1B strategic bombers in Japan.

 

Middle powers, particularly Australia and the UK, conducted some notable operations in the South China Sea. UK patrol vessel HMS Spey and Australian destroyer HMAS Sydney conducted a Freedom of Navigation (FON) Activity around the Spratly Islands on June 23 – the first time two countries conducted a joint activity publicly dubbed “FON” in the South China Sea. Australian warships conducted one “joint sail” with the U.S. (April 24) and one “routine transit” with the U.S. (September 15-16).

 

 

For example, when China announced its plans to establish a 3,523-hectare National Nature Reserve at the disputed Scarborough Shoal, dividing the feature into core, experimental, and main protection zones under the State Council’s approval, political opposition immediately followed. The Philippines lodged a diplomatic protest, calling the shoal its traditional fishing ground, while the U.S. issued a strong statement of support, describing China’s move as “coercive” and reaffirming the binding effect of the 2016 Arbitral Tribunal Award.²⁴

 

The South China Sea continues to be attached to major powers’ competition. U.S. officials have repeatedly raised the South China Sea in bilateral and multilateral diplomatic settings in 2025, condemning China’s actions after “clashes” on February 11 (with Australia), 18 February (with the Philippines at Scarborough), and May 21 (with the Philippines near Sandy Cay). The Trump 2.0 Administration further labelled China an “existential threat,” and outlined an approach to the Indo-Pacific region that included greater forward deployments, enhanced defense-industrial cooperation with allies and partners, and the “re-establishment” of deterrence.²⁵

From the other side, China has a different viewpoint. For China, Philippine activities in the South China Sea are violations of its sovereignty, and the U.S. is an extra-regional factor that stirs up troubles. Following a mid-October clash between Chinese and Philippine vessels, after which the U.S. reiterated the Mutual Defense Treaty in support of the Philippines, China accused the U.S. of “stoking confrontation and destabilizing” the South China Sea, deeming the latter as “the biggest source” of regional instability.²⁶

 

 

The so-called “Note Verbale Battle” at the United Nations, where countries circulate back and forth documents detailing their position regarding the South China Sea dispute, was started in 2009. The second round was ignited in 2013, and the third in 2019.²⁷

 

In 2025, we have witnessed the fourth round of such interaction, indicating the “battle” has re-emerged at the United Nations. China circulated three notes verbales reiterating its “Nanhai Zhudao” (South China Sea Islands) position, rejecting U.S. diplomatic notes, defending the use of straight baselines around offshore archipelagos, and dismissing the 2016 Arbitral Award. In response, the UK, Germany, and France (March 10) submitted a joint note rejecting China’s claims. Vietnam issued Note Verbale No. 85/CH-2025 to oppose China’s position and announced its new baseline declaration for the Gulf of Tonkin. On March 19, the Philippines submitted a note to the UN rejecting the “nine-dash line.”²⁸

 

 

We have not mentioned the informational domain, which has seemed to be a rising dimension within the South China Sea tension. Notably, the Philippines have continued to advance their so-called “transparency” strategy by publishing videos and images of incidents with Chinese vessels in the South China Sea, aiming to shape international opinion. China, in turn, released ecological survey reports blaming Philippine activities for coral degradation at Sandy Cay and Whitsun Reef.²⁹ Chinese state media also portrayed the Scarborough “nature reserve” plan as a conservation measure,³⁰ while the U.S. and Philippines denounced it as a tactic to legitimize illegal claims.³¹

 

Competition also extended to the economical and technological domains. China in 2025 officially announced their new deep-sea cable-cutting technology and plans to build a 6,000-foot underwater research station,³² alongside the development of the world’s first submarine-launched unmanned systems,³³ indicating a possibility of future warfare expanding to deeper ocean depth.³⁴ Meanwhile, the Trump 2.0 administration issued an executive order authorizing U.S. companies to unilaterally explore and exploit deep-sea resources, explicitly framing the move as a response to China. At the same time, Washington imposed steep tariffs on China and Southeast Asian economies, with U.S.-China reciprocal tariffs reaching as high as 125–145%, potentially affecting major powers’ dynamic and the international order in the Pacific region,³⁵ including in the South China Sea.³⁶

 

 

The South China Sea remains one of the most strategically vital and politically sensitive maritime regions in the world. Stretching across critical sea lines of communication, it is a conduit for global trade, a repository of marine biodiversity, and a space where sovereign claims, national pride, and geopolitical competition intersect. It also carries the weight of UNCLOS, as principles of maritime rights, freedom of navigation and environmental protection all converge in this single space. Despite numerous attempts at management, the South China Sea has become increasingly fragile, rooted in the unpredictable actions of major powers, unmanaged flashpoints from emerging hotspots, and unfamiliar domains from new technologies, new security frontiers and norms. The South China Sea has not been marked with an all-out armed conflict witnessed in other maritime bodies, such as the Red Sea or the Black Sea, but in the face of the above-mentioned uncertainties, even a small spark in any maritime area can bear consequences to the South China Sea and vice versa.

 

Against this backdrop, the South China Sea International Conference was first convened in 2009 and has since become one of the region’s leading forums on maritime security. Each year, it gathers policymakers, scholars, diplomats, legal experts, and media from Vietnam and around the world to exchange views, build trust, and identify opportunities for cooperation. Last year, the 16th Conference, held in Ha Long, Quang Ninh, under the theme “Navigating Narratives, Nurturing Norms,” attracted nearly 300 participants, including 50 distinguished speakers from 23 countries and international organizations, as well as ambassadors, foreign representatives, and extensive media coverage.

 

This year, the 17th South China Sea International Conference takes place in Da Nang, one of Vietnam’s most vibrant coastal cities, under the theme “Unity in Uncertainties.” The Conference  convenes regional and international scholars, policymakers, legal experts, diplomats, military officers, journalists, and young leaders to engage in open and constructive dialogue on current trends, emerging challenges, and practical ways forward. “Unity in Uncertainties” emphasizes the need to look beyond zero-sum competition and challenges stakeholders to recommit to shared interests: international laws and norms, freedom of navigation, peaceful resolution of disputes, marine environmental protection, and regional development. While consensus is never easy, the absence of unity has often proven far more costly. In such a  context, the Conference provides a critical platform for exchanging views, building trust, and identifying areas where meaningful cooperation is both possible and imperative. All these efforts ultimately lead us back to the central question: Is the South China Sea still important in today’s uncertain world?

 

In the end, the South China Sea in this past year might have appeared as a “dead calm” on the surface, but it was brewing with undertows in reality, thanks to stakeholders’ engagements on multiple fronts. This trend also shows that this is still an area that holds interest, where every manifestation of competition and cooperation serves as a reminder that this maritime domain remains a strategic space of enduring significance. In today's context of growing uncertainties, stemming from intensified great power rivalry and militarization to the increased use of grey-zone tactics and disruptive technologies such as AI and unmanned systems, these very uncertainties call for a renewed unity in principles, practices, and partnerships, so that peace and stability may be preserved, and the rule of law upheld. As long as players, including policy makers, practitioners, experts, and citizens from across the world, choose to come together in dialogue, the South China Sea will remain more than a contested maritime space; it will remain a common responsibility and a common hope to be managed through cooperation and shared vision.

 

REFERENCE

1.https://www.fmprc.gov.cn/eng/xw/fyrbt/lxjzh/202504/t20250411_11593654.html
2. Ibid
3. Ibid
4.https://www.mfa.gov.cn/eng/xw/wjbxw/202501/t20250117_11537079.html
5.https://www.scmp.com/news/china/diplomacy/article/3297849/maritime-rivals-china-and-brunei-vow-work-together-oil-and-gas-disputed-waters
6.https://english.www.gov.cn/news/202505/25/content_WS6832d6abc6d0868f4e8f2d43.html
7.https://asean.org/wp-content/uploads/2025/08/Final-ASEAN-China-POA-2026-2030.pdf
8.https://asean.usmission.gov/fact-sheet-president-donald-j-trump-secures-peace-and-prosperity-in-malaysia/
9.https://asean.org/asean-united-states-leaders-joint-vision-statement-to-promote-stronger-safer-and-more-prosperous-asean-and-america/
10.Compiled by Center for Information and Data Analysis, South China Sea Institute, Diplomatic Academy of Vietnam
11.https://www.state.gov/the-united-states-commitment-to-maritime-security-in-the-indo-pacific
12.https://maritimefairtrade.org/philippines-u-s-launch-p140-million-maritime-training-to-boost-security/
13.https://navalinstitute.com.au/china-singapore-exercise-cooperation-2025/
14. Compiled by the Center for International Law, South China Sea Institute, Diplomatic Academy of Vietnam
15. Compiled by Center for Maritime Diplomacy, South China Sea Institute, Diplomatic Academy of Vietnam
16. Compiled by Center for Information and Data Analysis, South China Sea Institute, Diplomatic Academy of Vietnam
17. Compiled by Center for Information and Data Analysis, South China Sea Institute, Diplomatic Academy of Vietnam.
18. Compiled by the Center for International Law, South China Sea Institute, Diplomatic Academy of Vietnam. For information on Vietnam’s signing of the BBNJ, please visit: https://en.vneconomy.vn/vietnam-among-first-countries-to-sign-high-seas-treaty.htm
19.https://www.cnn.com/2025/04/28/asia/china-philippines-sandy-cave-dispute-intl-hnk
20.https://www.inquirer.net/445014/china-coast-guard-sideswipes-uses-water-cannon-on-bfar-boat/#:~:text=The%20Datu%20Sanday%20and%20another,1%2C%202%2C%20and%203.
21.https://www.bbc.com/news/videos/c1jnne45dj3o
22.Compiled by the Center for Political and Security Studies, South China Sea Institute, Diplomatic Academy of Vietnam
23.Compiled by Center for Information and Data Analysis, South China Sea Institute, Diplomatic Academy of Vietnam
24.https://www.state.gov/releases/2025/09/on-scarborough-reef
25.https://www.war.gov/News/Speeches/Speech/Article/4202494/remarks-by-secretary-of-defense-pete-hegseth-at-the-2025-shangri-la-dialogue-in/
26.https://www.aa.com.tr/en/asia-pacific/china-accuses-us-of-deliberately-destabilizing-south-china-sea/3717711
27.https://www.lawjournals.org/assets/archives/2025/vol11issue5/11104.pdf
28.https://www.un.org/depts/los/clcs_new/submissions_files/phl1/20250319Phl1NvUn004.pdf
29.https://www.scmp.com/news/china/diplomacy/article/3307920/south-china-sea-china-blames-philippine-activity-coral-damage-disputed-sandy-cay
30.https://www.globaltimes.cn/page/202509/1343192.shtml
31.https://dfa.gov.ph/dfa-news/statements-and-advisoriesupdate/37142-dfa-statement-on-china-s-recent-approval-of-the-establishment-of-a-nature-reserve-in-bajo-de-masinloc
32.https://www.scmp.com/news/china/science/article/3303246/china-unveils-powerful-deep-sea-cable-cutter-could-reset-world-order
33.https://english.news.cn/20250428/1d947fe891dd496ab8c782d8879c9717/c.html
34.https://www.scmp.com/news/china/military/article/3327870/chinese-militarys-new-underwater-unmanned-systems-are-disruptive-intelligent-journal 
35.https://www.chathamhouse.org/2025/04/trumps-tariffs-will-push-southeast-asia-uncomfortably-close-china
36.https://thediplomat.com/2018/11/how-the-us-china-trade-war-could-impact-the-south-china-sea/