Turbulent Waters Remain Top of Mind

Southeast Asian countries are grappling with many pressing challenges, but one issue remains top of mind — the South China Sea (SCS). Frequent flare-ups in the disputed waters between the Philippines and China over the last year have caused much consternation in the region, particularly among the claimant states*. These developments resonated uneasily with Chinese Foreign Minister Wang Yi’s remarks in March when he warned that “major powers should not act out of self-interest, nor should they bully the weak with their strength”. Though aimed at US ambitions to acquire Greenland and the Panama Canal, Wang’s statement lands closer to home than intended. In its own neighbourhood, smaller nations are growing wary of China’s assertive posture in the SCS.

According to the State of Southeast Asia Survey 2025 (SSEA 2025), aggressive behaviour in the SCS was the top geopolitical problem for 51.6 per cent of respondents. They also flagged China’s encroachments in the exclusive economic zones of other littoral states (48.2 per cent), the risk of political crisis arising from an incident between an ASEAN country and China (44.30 per cent), and China’s militarisation and assertive actions (40.6 per cent) as their greatest concerns regarding the SCS.

When asked what China could do to improve relations with Southeast Asian countries, the most common response was for Beijing to resolve these disputes peacefully in accordance with international law (33.10 per cent). This echoed findings from prior iterations of the survey. Evidently, regional concerns over the SCS are genuine and home-grown, countering Beijing’s assertion that tensions in the disputed waters are merely fuelled by American interference.

Aggressive Behaviour a Top Concern

Most respondents support ASEAN taking a principled stand that upholds international law, including the United Nations Convention on the Law of the Sea (UNCLOS) and the 2016 arbitral tribunal’s award on the SCS (69.5 per cent), which ruled China’s nine-dash line claims were illegal. Despite ASEAN’s disunity on this matter, its agency remains valued — only 13.3 per cent of respondents believe that ASEAN cannot do anything. Of note, respondents from non-claimant states (18.7 per cent) were generally more dismissive of ASEAN’s role on the SCS issue than the claimant states (8.0 per cent).

ASEAN Retains Some Agency

The second-most preferred option was to deter aggressive behaviour through joint military exercises (46.1 per cent). Given the rarity of intra-ASEAN maritime exercises — the ASEAN Solidarity Exercise 2023 being a recent example — many regional drills are led by or involve external powers. Yet, there is a general wariness about the military presence of external powers in the SCS, with only 12.7 per cent supporting this option. This illustrates the dilemma of Southeast Asian states’ “Goldilocks” policy, which aims to strike a regional strategic balance that is neither too hot nor too cold. They recognise the need for deterrence, which inevitably requires external power involvement, while concurrently fearing that entanglement with great power rivalry could escalate into broader conflict, causing more tension than stability.

Notably, key Southeast Asian claimant states exhibit varying degrees of preference regarding external involvement in the SCS. Mirroring their leaders’ occasional rhetoric on this matter, Bruneian (28.2 per cent), Indonesian (24.2 per cent), and Malaysian (25.4 per cent) respondents were more inclined to exclude external parties. This reflects an enduring strand of their strategic thought rooted in the 1971 Zone of Peace, Freedom, and Neutrality, which emphasises regional autonomy and discourages external intervention. Nevertheless, both Indonesia and Malaysia remain active in major military exercises involving extra-regional powers — Jakarta has expanded the bilateral Garuda Shield Exercises into the multilateral Super Garuda Shield, while Kuala Lumpur participates in Exercise Bersama Lima as part of the Five Power Defence Arrangements.

Diverging Views among South China Sea Claimant States

Conversely, Vietnamese and Filipino respondents appear to be more welcoming of foreign powers’ involvement to achieve a more favourable balance of power. This is due to their greater threat perception vis-à-vis China in the SCS. A significant majority of Vietnamese (74.8 per cent) and Filipino (90.3 per cent) respondents identify the SCS dispute as their country’s top geopolitical concern. Many Vietnamese (54.4 per cent) and Filipino (46.2 per cent) respondents also indicate that their perceptions of Beijing will worsen if China uses strong-arm tactics in the SCS (and the Mekong).

As ASEAN and China continue their prolonged negotiations on a Code of Conduct (COC) in the SCS, international law remains the guiding principle for regional states, reinforcing their stance that ASEAN should uphold a principled position. Some 41 per cent of respondents prefer that a future COC be aligned with international law, including UNCLOS, with the strongest support from Vietnam (63.2 per cent), the Philippines (54.4 per cent), and Indonesia (48.0 per cent).

Still, respondents are generally pessimistic about the prospects for an effective COC. Only 14.4 per cent think it would help reduce tensions and manage the dispute, while 13.4 per cent believe that the COC would not even materialise given Beijing’s insistence on its claims based on the nine-dash line. Among the claimant states, Vietnam (10.3 per cent) and the Philippines (10.7 per cent) are the most sceptical about the COC’s effect, whereas Indonesia (13.9 per cent), Malaysia (20.4 per cent), and Brunei (16.1 per cent) are relatively more optimistic.

Another notable finding is that mainland Southeast Asian respondents, except for Vietnam, generally think that the COC will restrict other powers from conducting military activities and energy exploration with regional states in the SCS — two contentious provisions inserted by China in the negotiations that have drawn opposition from extra-regional powers. In contrast, most maritime states, except Brunei, are less convinced that these restrictions will materialise. Given that the latter states have the most to lose from limitations on military exercises and energy exploration with extra-regional powers, China faces an uphill battle in pushing these provisions through.

The SSEA 2025 survey findings underscore the genuine regional concerns regarding Chinese actions in the SCS, especially among Southeast Asian claimant states — a reality that China continues to downplay or obscure with its dominant power and narrative. Leaders of Southeast Asian claimant states, wary of jeopardising broader bilateral ties, often hesitate to challenge China directly and opt for more cooperative approaches. However, the SCS disputes will continue to be a perpetual thorn in the side of China’s regional image. Over different iterations of the SSEA survey, the region’s message to China remains clear and consistent, but whether Beijing will hear and act on it remains to be seen.

*Indonesia is not a claimant state in terms of sovereignty over the disputed islands in the SCS, but it has a dispute with China’s claim of maritime rights and interests in the waters off Indonesia’s Natuna Islands. For simplicity, this article includes Indonesia in the list of claimant states.

Hoang Thi Ha is Senior Fellow and Co-coordinator of the Regional Strategic and Political Studies Programme, ISEAS – Yusof Ishak Institute.

Eugene R.L. Tan is a Research Officer with the Regional Strategic and Political Studies Programme at ISEAS – Yusof Ishak Institute.

This article originally appeared on Fulcrum on 15 April 2025.