Philippines President Rodrigo Duterte on Monday condemned the latest flare-up in the disputed South China Sea (SCS) after Chinese coastguard ships fired water cannon at Filipino boats.
Duterte made the remarks at an Asian regional summit hosted by Chinese President Xi Jinping, who vowed his country would "never seek hegemony, and certainly not bully the small".
China claims almost all of the waterway, through which trillions of dollars in trade passes annually, with competing claims from Brunei, Malaysia, the Philippines, Taiwan and Vietnam.
Beijing has ignored a 2016 ruling by The Hague-based Permanent Court of Arbitration (PCA) that its historical claim is without basis.
Tensions over the resource-rich sea spiked last week when Chinese coastguard vessels fired water cannon at Philippine boats delivering supplies to Filipino marines on Second Thomas Shoal, in the contested Spratly Islands.
Manila expressed outrage at the incident, but Beijing said the Philippine boats had entered its waters without permission.
"We abhor the recent event in the Ayungin Shoal and view with grave concern other similar developments," Duterte told the meeting of the Association of Southeast Asian Nations (ASEAN) and China, using the Filipino name for the shoal.
"This does not speak well of the relations between our nations and our partnership."
Duterte's remarks were unusually strong for a leader who has fostered warmer ties with Beijing since taking power in 2016 in the hope of extracting promised investment and trade.
It is not clear if Xi was participating in the meeting when Duterte spoke.
For his part, Xi told the gathering "we must jointly maintain the stability of the South China Sea and build the South China Sea into a sea of peace, friendship, and cooperation".
Meanwhile, Myanmar's junta said it was not represented at the summit after some ASEAN members blocked an invitation from China for its chief to attend.
It was the second time in weeks that Min Aung Hlaing had been excluded from an ASEAN gathering, deepening the regime's isolation after it took power in a coup earlier this year.
The renewed tensions over the SCS have drawn international concern.
The United States (US) on Friday warned China that an armed attack against Philippine public vessels would invite a US response under its treaty obligations to the Southeast Asian nation.
The European Union (EU) also called on "all parties to respect freedom of navigation and overflight in the South China Sea".
At the summit, Malaysian Prime Minister Ismail Sabri Yaakob warned against actions that could "further complicate the situation and escalate tensions in the area".
Duterte said the UN Convention on the Law of the Sea (UNCLOS) and the 2016 arbitral ruling against China –which he set aside after taking office – should be "fully" utilised to resolve the disputes.
He urged China to "remain committed to the early conclusion of an effective and substantive Code of Conduct in the South China Sea".
"There is simply no other way out of this colossal problem but the rule of law," he added.
Philippines Defence Secretary Delfin Lorenzana said the supply boats would resume their mission to Second Thomas Shoal after China's ambassador to the Philippines gave assurances they would not be impeded.
China controls several reefs in the SCS including Scarborough Shoal – which Beijing seized from Manila in 2012 – just 240 kilometres (150 miles) west of the main Philippine island of Luzon.
It has asserted its stance by building up small shoals and reefs into military bases with airstrips and port facilities.
After China occupied Mischief Reef in the mid-1990s, the Philippines marooned a derelict navy vessel atop the nearby Second Thomas Shoal to assert Manila's territorial claim. Members of the Philippine marines are based there.