By Carlyle A. Thayer
The geo-politics of the South China Sea in 2025 were shaped by four trends: continued confrontations between the China Coast Guard (CCG) and claimant states; renewed construction and militarization of features in the South China Sea; major demonstrations of naval power by China, the United States and other maritime powers; and progress on the ASEAN-China Code of Conduct (CoC) in the South China Sea.
China Confronts Littoral States
In 2025 there was a marked change in the deployment of CCG vessels to Scarborough and Sabina Shoals in the West Philippine Sea. According to a detailed report issued by the Center for Strategic and International Studies’ (CSIS) Asia Maritime Transparency Initiative (AMTI), the CCG “maintained an unprecedented level of presence at Scarborough Shoal in 2025. The total number of CCG ship days more than doubled from 516 in 2024 to 1,099 in 2025, with patrols observed on 352 calendar days.” CCG patrols around Sabina Shoal nearly tripled from 139 to 405 in 2025 and covered a wider area than previously. In April, the CCG temporarily landed on Sandy Cay and in October, CCG vessels used high-pressure water cannons and ramming against Filipino fishing craft at Pag-asa Island and Sabina Shoal.
At the same time, the CCG decreased its presence at Pag-asa and Second Thomas Shoal in Philippine waters as well as at Luconia Shoal (Malaysia) and Vanguard Bank (Vietnam). Nevertheless, the CCG continued to monitor oil and gas activities around Vanguard Bank, accost Vietnamese fishing boats near the Paracel Islands, and harass drilling rigs and survey ships in waters off Sarawak and Indonesia’s North Natuna Sea. The CCG also escorted Chinese fishing boats in the North Natuna Sea where Bakamla (Indonesia’s Maritime Security Agency) reported a rise in illegal, unreported and unregulated fishing.
Further Militarization of Features
In 2025, Vietnam markedly accelerated its landfilling efforts on twenty-one features in the Spratly Islands including eight previously undeveloped features by creating nearly nine square kilometers of new land. Vietnam also stepped up its construction of infrastructure by dredging harbors and erecting piers, docks, reinforced embankments, buildings, and storage facilities. The most significant development was the doubling of the land area on Barque Canada Reef to 1.6 square km and construction of 3.2 km runway. The total land area of Vietnam’s features in the Spratly Islands is about seventy percent of the area currently occupied by China.
According to the CSIS AMTI, Vietnam’s new infrastructure is designed to enhance its logistics and defense capabilities and includes military barracks, trenches, munition storage, and docks capable of berthing Gepard-class missile frigates.
In October, China commenced dredging and landfill activities at Antelope Reef in the Crescent Groups of the Paracels Islands. By the end of the year a roll-on/roll-off berth and access road has been completed. Military analysts speculated that China was expanding its capability both to deny the United States the ability to gather intelligence on Chinese activities and to disrupt U.S. military activities in case of a Taiwan contingency.
Naval Balance of Power
The U.S. Navy deployed four Carrier Strike Groups (CSG) to the South China Sea during 2025 where they conducted routine patrols and participated in exercises with allied navies. The Nimitz CSG carried out advanced flight operations in June and October and conducted a trilateral exercise with Japan and the Philippines in November. The Carl Vinson CSG deployed in July and returned to San Diego in mid-August. The George Washington CSG made a port visit to Manila in July and relieved the Nimitz CSG in November. The Abraham Lincoln CSG deployed to the South China Sea in December and conducted live-fire drills and replenishment-at-sea operations before deploying to the Middle East.
In 2025, the U.S. Navy decreased the number of its Freedom of Navigation Operational Patrols (FONOPS) from an average of five to seven between 2017 and 2024 to two. In June, the USS Princeton transited the Spratly Islands and in August the USS Higgins sailed through the waters near Scarborough Shoal.
The Royal Australian Navy (RAN) conducted four Regional Presence Deployments to the South China Sea during 2025 involving three guided-missile destroyers (HMAS Hobart, HMAS Sydney, and HMAS Brisbane) and a frigate (HMAS Ballarat). The RAN ships conducted joint activities with the Philippines, New Zealand and U.S. navies.
In August, a United Kingdom CSG deployed to the South China Sea and conducted joint operations with the RAN, Japan Maritime Self-Defense Force (JMSDF) and the U.S. Navy in the Philippine Sea and South China Sea.
The People’s Liberation Army Navy (PLAN) also deployed its aircraft carriers to the South China Sea to demonstrate its growing military capacity. In June, the Liaoning and Shandong deployed simultaneously to the South China Sea and Western Pacific to take part in opposing forces exercises. In September, the Fujian (Type-003) aircraft carrier equipped with an electromagnetic catapult conducted its ninth and final sea trial in the South China Sea. The Fujian officially commissioned into the PLAN in November.
The PLAN carried out a live-fire exercise near Scarborough Shoal in October to coincide with two maritime exercises carried out by the Philippines, United States and other navies in the West Philippine Sea, Sama Sama 2025 and a Maritime Cooperative Activity.
Progress on the Code of Conduct
In 2025, Malaysia took on the role of ASEAN Chair. Malaysia was also ASEAN’s country coordinator for relations with China. In this dual capacity, Malaysia stepped up the pace of negotiations on a Code of Conduct in the South China Sea. Normally, ASEAN and China would hold two annual meetings of the Joint Working Group to Implement the Declaration on Conduct of Parties in the South China Sea (JWG-DOC). In 2025, five JWG-DOC meetings were held.
In August, the 48th JWG-DOC and 24th ASEAN-China Senior Officials Meeting were held in Kuching, Malaysia. ASEAN and Chinese officials agreed on a schedule to complete negotiations. At Malaysia’s initiative a rapid discussion group was formed to keep momentum going. Later, Malaysia’s foreign minister, Datuk Seri Mohammad Hasan, announced that negotiations with China “made significant progress, with nearly 70 per cent of the content agreed upon…”
Looking to the Future
Now that the negotiations on a Code of Conduct in the South China Sea are entering their final phase with a putative deadline set for the end of 2026, external pressure will mount on both China and the Philippines to act with self-restraint and lower tensions in the South China Sea.
The surge of the CCG into the waters around Scarborough Shoal and Vietnamese construction activities in the Spratlys in 2025 appear motivated in part to create a new status quo before a final Code of Conduct is agreed. Likewise, displays of naval power by the United States and China also serve to constrain any escalation that would lead to overturing the status quo.
In sum, geopolitical tensions in the South China Sea should subside in the coming year if the final thirty percent of the Code of Conduct can be negotiated. Progress on the final tranche would provide a clearer framework for crisis management and maritime cooperation, even as underlying disputes persist.
Carlyle Thayer is Emeritus Professor at The University of New South Wales at the Australian Defence Force Academy, Canberra and Director of Thayer Consultancy, a small business registered in Australia. Thayer is a member of the South China Sea NewsWire’s Advisory Board.
