Tensions in the South China Sea and China's accelerating military expansion took centre stage at the ASEAN Defence Ministers' Meeting-Plus (ADMM-Plus) held in Cebu, Philippines, as a diplomatic dispute between Beijing and Manila over China's participation cast a shadow over the forum.

Australia Sounds the Alarm on China's Military Growth

Australian Defence Minister Richard Marles, speaking on the sidelines of the ADMM-Plus, described China's military expansion as the largest conventional military build-up witnessed since World War II. Marles flagged Beijing's growing assertiveness as a direct challenge and called for tighter coordination among like-minded partners and allies.

'We need to be ensuring that how we understand the rules of the road continues to apply, because for a middle power like Australia, it is actually the rules which give us agency,' Marles said.

Australia had earlier this year protested China's test-firing of a nuclear-capable ballistic missile in the South Pacific in July, denouncing the launch as 'provocative and destabilising,' according to reports.

Beijing-Manila Dispute Spills Into Diplomatic Row

The maritime dispute between China and the Philippines extended well beyond the sea and into the summit itself. China's Ministry of Defence accused the Philippines of obstructing Beijing's participation in the ADMM meetings and violating 'basic diplomatic protocols.' Chinese Defence Minister Dong Jun subsequently skipped the meeting entirely.

China was instead represented by its defence attaché — marking the lowest-level Chinese representation at the ADMM-Plus since the forum's inception in 2010. The ADMM-Plus brings together defence ministers from ASEAN's 11 member countries and its eight dialogue partners: Australia, China, India, Japan, New Zealand, Russia, South Korea, and the United States.

Philippine Defence Secretary Gilberto Teodoro declined to respond directly to Beijing's allegation, saying China was 'given an opportunity to articulate their position, which is not any different from what they have been articulating before.'

Escalating Confrontations in Contested Waters

According to reports, China has significantly increased both the frequency and intensity of its incursions into areas of the South China Sea claimed by the Philippines in recent years, resulting in a string of increasingly dangerous confrontations. The flashpoints have been particularly acute around Scarborough Shoal and Second Thomas Shoal in the Spratly Islands.

These incidents reflect what analysts describe as a 'condition of pressure' that China's military posture is creating across Southeast Asia — a phrase Marles himself used in his remarks to the media.

What This Means for Regional Security

China's decision to downgrade its representation at ADMM-Plus is widely seen as a signal of its deepening frustration with Manila and, by extension, with US-allied partners in the region. Notably, this comes at a time when Washington has been strengthening its defence partnerships with both the Philippines and Australia under various bilateral and multilateral frameworks.

The poor state of Beijing-Manila relations — frayed by repeated at-sea confrontations — now risks undermining the ASEAN-led multilateral security architecture, which has historically sought to manage great-power rivalry through dialogue rather than confrontation. With China's defence minister absent and no sign of de-escalation, the South China Sea's trajectory into the coming months remains deeply uncertain.