The Philippines' foreign minister on Thursday denounced Chinese "duplicity" and "intimidation" in the South China Sea, souring the mood at a regional gathering designed to soothe tensions.

"If Philippine sovereignty and jurisdiction can be denigrated by a powerful country through pressure, duplicity, intimidation and the threat of the use of force, the international community should be concerned about the behaviour," Albert del Rosario told the meeting, according to an official statement.

He was referring to a recent standoff between Chinese and Philippine boats at a rocky outcrop called the Scarborough Shoal, which is claimed by both sides.

Del Rosario said Beijing's increasingly assertive stance over disputed and non-disputed areas of the South China Sea posed a "threat to the peace and stability" in the Asia Pacific region.

"If left unchecked, the increasing tensions that is being generated in the process could further escalate into physical hostilities which no one wants," he said at the ASEAN Regional Forum, which was also attended by Chinese Foreign Minister Yang Jiechi and US Secretary of State Hillary Clinton.

The dispute over Scarborough Shoal began after Chinese government vessels blocked Philippine ships in an operation to arrest Chinese fishermen near the shoal on April 10.

China claims nearly all of the South China Sea, even waters close to the coasts of neighbouring countries. The Philippines says the shoal is well within its 200-nautical-mile exclusive economic zone.

A sharp disagreement over whether to mention the standoff over the shoal has held up a joint statement being prepared by the Association of Southeast Asian Nations (ASEAN).

Manila wants the standoff mentioned while Cambodia, a staunch Chinese ally that currently holds the ASEAN chair, has rejected the proposal.

The Philippines is also leading a push for ASEAN to unite to propose to China a code of conduct aimed at governing behaviour and preventing conflicts in the South China Sea.

Progress on the code, strongly encouraged by the United States, was seen by analysts as a way of dissipating anger in the region and smoothing tensions after a string of recent confrontations.

Vietnam has accused China of aggressive behaviour and on Wednesday Japan lodged a formal complaint over Chinese boats approaching islands in the East China Sea which are controlled by Tokyo.

ASEAN has already agreed the key elements it will propose in any negotiations with China, including using international law such as the UN Convention on the Law of the Sea as the basis for any dispute.

But analysts said Beijing was likely to reject any use of international law to settle disputes because its position is to deal bilaterally with each claimant.

Yang has told his fellow ASEAN ministers in Cambodia that China will consider the proposal but stressed that negotiations for a code of conduct will only be launched when "conditions are ripe".

Clinton said earlier Thursday that nations should settle their territorial disputes "without coercion, without intimidation, without threats, and without use of force".

She also urged progress on the long-stalled code of conduct for the South China Sea to avoid "confusion and even confrontation" over shipping and fishing rights in the resource-rich waterway which is home to key shipping lanes.

The Scarborough Shoal sits about 230 kilometres (140 miles) from the Philippines' main island of Luzon. The nearest major Chinese landmass is 1,200 kilometres northwest of the shoal, according to Philippine navy maps.