On February 24, 2025, China launched a live-fire military exercise in the Gulf of Tonkin (as Vietnam calls it), just days after Vietnam announced a new baseline defining its territorial waters in the area. Beijing’s move came at the same time that international media focused on the warming relationship between the two superpowers, Russia and the United States, under Trump 2.0. The Ukrainian battlefield has become a place of interest for major countries because of how much benefit they will gain from a war that has been preparing for its end for three years. While Washington is focusing on Europe—the Atlantic, and in Asia—the Pacific, Beijing is taking advantage of the international community’s distraction to carry out military actions in the first months of 2025.
Information about the exercise
On February 21, 2025, the China Maritime Safety Administration (MSA) issued a notice to hold a live-fire exercise in the Gulf of Tonkin. According to the notice, the exercise will take place from 8:00 a.m. on February 24 to 6:00 p.m. on February 27, 2025, local time. The exercise area is located northwest of Hainan Island, about 150 km from Vietnam’s Bach Long Vi Island. The MSA has also warned vessels to stay away from this area during the exercise to ensure maritime safety.
This exercise took place right after Vietnam announced the new baseline defining its territorial waters in the Gulf of Tonkin on February 21, 2025. Accordingly, based on Resolution No. 68/NQ-UBTVQH15 dated February 14, 2025, of the National Assembly Standing Committee, the Government of the Socialist Republic of Vietnam issued a declaration on the baseline used to calculate the breadth of Vietnam’s territorial waters in the Gulf of Tonkin.
Vietnam has sufficient legal basis to strengthen its sovereignty and jurisdiction in the region, in accordance with the United Nations Convention on the Law of the Sea (UNCLOS). China’s quick conduct of live-fire drills right after Vietnam’s announcement was assessed by commentator David Rising of AP News as a direct response by Beijing to show its disagreement with Hanoi’s sovereignty claim.
Reaction from stakeholders
In the past year, 2024, some disputes related to the South China Seaand strategic competition between major powers continue to be predicted by many scholars to be the focus of major security issues in the Asia-Pacific region. As expected, China’s first live-fire military operation in the South China Sea in early 2025 took place in the context of increasing tensions between Beijing and neighboring countries over sovereignty disputes. Therefore, this Chinese exercise has received many immediate harsh reactions from relevant parties.
Taiwan has strongly condemned the live-fire drills near its southwest coast, just 74 kilometers from the cities of Kaohsiung and Pingtung, especially since Beijing did not give prior notice of the military activities near the island’s southwest coast. Taiwan’s Ministry of National Defense said 32 Chinese aircraft were involved, many of which crossed the median line of the Taiwan Strait and entered Taiwan’s Air Defense Identification Zone (ADIZ). Taipei authorities stressed that the actions “seriously endangered” international maritime and aviation security and threatened regional peace and stability.
On the other hand, the Philippines has expressed concern over China’s unannounced military activities in the area that could endanger maritime and aviation security. The Philippines has repeatedly protested the presence and activities of Chinese vessels in waters it claims. China’s continued military exercises near disputed areas could further escalate tensions between the two countries, which have escalated since July 2024 over the dispute at Second Thomas Shoal. Recently, the French nuclear-powered aircraft carrier Charles de Gaulle participated in joint exercises with Philippine forces in the South China Sea, aiming to improve readiness and ensure regional security.
In response to the incident in the Gulf of Tonkin, on February 22, a report from the New Zealand Defense Force said that three warships of the People’s Liberation Army Navy (PLAN) conducted live-fire exercises in international waters between Australia and New Zealand, causing disruption to the aviation industry. Airlines, including Qantas, Emirates, Air New Zealand, and Virgin Australia, adjusted their flight routes on February 21 after China warned them about the exercise. The Australian government expressed concern about the lack of advance notice from China, while China insisted that it had complied with international law and issued a safety notice in advance. The New Zealand government expressed concern about the lack of advance notice from China, saying that this could lead to misunderstandings and increase the risk of unintended conflict.
Vietnam’s response
At the regular press conference of the Ministry of Foreign Affairs on the afternoon of February 27, Spokesperson Pham Thu Hang officially responded to China’s military exercise in the Gulf of Tonkin. Vietnam had information in advance after the China Maritime Safety Administration issued Notice No. 13/2025 to conduct the exercise from February 24 to 27. In addition, the area where China announced the exercise is located in the waters under China’s management in the Gulf of Tonkin and does not affect Vietnam’s sovereignty.
Before the exercise, on February 21, Vietnam announced a new baseline defining its territorial waters in the Gulf of Tonkin. Accordingly, “The baseline used to calculate the breadth of Vietnam’s territorial waters in the Gulf of Tonkin is determined on the basis of the provisions of the 1982 United Nations Convention on the Law of the Sea (UNCLOS) and the Agreement on the Delimitation of the Gulf of Tonkin between Vietnam and China signed in 2000, in accordance with the geographical and natural characteristics of the Gulf of Tonkin, and does not affect international treaties to which Vietnam is a party or participant.” The clear determination of the baseline in the Gulf of Tonkin creates an additional legal basis to protect and exercise Vietnam’s sovereignty, sovereign rights, and jurisdiction, contributing to economic development and maritime management and promoting international cooperation in the coming time.
With all the above grounds, the fact that Vietnam has not responded immediately after China’s military exercise shows some harmony in the following diplomatic handling. First, an immediate harsh reaction can give rise to bilateral tensions, affecting dialogue channels. Vietnam chooses a calm, cautious, observant approach based on international law. Second, Vietnam prioritizes the use of active bilateral diplomatic channels and consultation mechanisms between the two countries’ foreign ministries to work to avoid unnecessary tensions. Third, a strong reaction can be interpreted by the parties as confrontation or alliance with other parties to counterbalance China. Instead, Vietnam chooses to monitor the moves of major countries, especially the US, before making an official response.
Just two days after the exercise, Vietnam upgraded its Comprehensive Strategic Partnership with New Zealand, with the full text of the upgraded bilateral relationship noting that security and defense cooperation was given a high priority. This shows that Vietnam may be using practical actions to strengthen its defense capabilities, instead of just reacting with diplomatic statements. Over the past year, Vietnam has had three more Comprehensive Strategic Partners, countries with strong military capabilities, including Australia, France, and New Zealand, with the common point in the full text of the upgraded relationship being that security and defense are all given a higher priority than economic, trade, and investment cooperation. Specifically, the issues of maritime security and freedom and increased defense exchanges regarding the South China Sea were emphasized. This is a big difference from when Vietnam upgraded its relations with the US or Japan in 2023.
Strengthening security and defense cooperation with comprehensive strategic partners such as Australia, France, and New Zealand shows that Vietnam is taking advantage of both consolidating its defense capacity and maintaining strategic balance. Hanoi is implementing a flexible diplomatic strategy, continuing to maintain the “four no’s” policy, making the most of resources from partners to protect national interests without necessarily joining alliances. While economic cooperation with the US and Japan helps Vietnam participate more deeply in the global value chain, promoting security and defense cooperation with middle-ranking countries in the Indo-Pacific region helps strengthen self-defense capacity in the face of increasing security challenges. These adjustments reflect Vietnam’s long-term strategic thinking in the context of a rapidly changing regional order, especially when China is conducting military activities in the South China Sea.
South China Sea situation in the coming time
Since 2016, after the final ruling of the Permanent Court of Arbitration (PCA), the situation in the South China Sea has generally tended to remain stable. However, in 2023, especially in 2024, this trend has been seriously challenged. The US, under the leadership of President Joe Biden, has continuously deployed militarization activities in the South China Sea with increasing scale in both rhetoric and action. Meanwhile, clashes between China and countries around the South China Sea have increased in intensity, mainly revolving around “gray zone” activities. With the Philippines increasing provocative actions in areas such as the Second Thomas Shoal, Sa Bin Shoal, and Scarborough Shoal. With Vietnam in the Hoang Sa archipelago. Objective and subjective factors in this region interact with each other, continuously increasing tensions in the South China Sea. That makes the trend of stability and improvement in the situation in the South China Sea difficult to maintain.
Along with that, the return of Donald Trump as US President will push the US-China strategic competition into a new climax. In addition to the trade tariff battlefield, the possibility of a real hotspot in the South China Sea cannot be ruled out.
Looking at Trump’s first term, it can be seen that Trump is not interested in US-led alliances; instead, Trump will prioritize “sub-multilateral alliance” activities based on “reciprocal” relations. Mechanisms based on the trio, such as “US – Philippines – Australia” or US – Australia – New Zealand (ANZUS), or the quadrilateral, such as “QUAD plus” (Vietnam, South Korea) or the US – Australia – New Zealand – Vietnam mechanism, will become the US policy priorities under Trump 2.0 for the Southeast Asia region in general and the South China Sea in particular. At the same time, the existing mechanisms under Biden, such as AUKUS and JAPHUS, will continue to have their content of operations modified by the US to suit reality. In the coming time, the adjustment of these cooperation mechanisms will cause the structure of force aggregation in the South China Sea to be continuously adjusted.
The continued impact of “external” factors and “internal” acceptance in the South China Sea will also lead to the acceleration of the militarization of the South China Sea. This is an opportunity for major countries such as the US and China to increase their military presence, along with the emergence of non-traditional warfare activities such as cyber attacks.
Conclude
China’s live-fire drills in the Gulf of Tonkin at a time when the war in Ukraine is entering its final stages can be seen as a strategy to take advantage of the international community’s distraction. This action is not only to strengthen China’s sovereignty claims in the South China Sea but also to send a strong message to countries in the region about its military presence and strength.
For Vietnam and some other Southeast Asian countries with interests in the South China Sea, the increase in China’s military activities since early 2025 poses a major challenge to regional sovereignty and security. The tense developments at sea are becoming the main factor reducing the effectiveness of international legal documents, such as the 1982 United Nations Convention on the Law of the Sea (UNCLOS) and the Declaration on the Conduct of Parties in the South China Sea (DOC). Therefore, countries in the region need to strengthen cooperation, strengthen defense capacity, and seek support from the international community to deal with these challenges.
