The Philippines accused China on Saturday of undermining peace and stability in Asia by allegedly sending naval vessels to intimidate rival claimants in disputed sections of the South China Sea.

Manila had protested over incidents in February to May, when the Chinese navy allegedly opened fire on Filipino fishermen, intimidated a Philippine oil exploration ship and put posts and a buoy in Philippine-claimed areas.

"The Philippines noted that these actions of Chinese vessels hamper the normal and legitimate fishing activities of the Filipino fishermen in the area and undermines the peace and stability of the region," Manila said.

"The actions of the Chinese vessels in Philippine waters are serious violations of Philippine sovereignty and maritime jurisdiction," said a statement issued by the foreign department.

Manila had also earlier queried Beijing over plans reported in Chinese state media to install an oil rig in the area.

The Chinese embassy in Manila on Thursday denied that Chinese naval vessels had intruded on Philippine territory, while reiterating Beijing's territorial sovereignty over the disputed South China Sea areas.

The Philippine foreign department statement said both governments agreed to continue dialogue on the highly sensitive issue.

Manila says the incidents happened in an area of the South China Sea just outside the Spratlys, a reputedly oil-rich island chain claimed in whole or in part by Brunei, China, Malaysia, the Philippines, Taiwan and Vietnam.

Some of these also have competing claims on the Paracel Islands, another South China Sea chain.

In May, Chinese ships confronted a Vietnamese oil exploration vessel between the Paracels and the Spratlys.

The renewed tensions drew a warning Saturday by the United States, the region's dominant naval power that is militarily allied with the Philippines, that the myriad territorial disputes could lead to armed conflict.

US Defence Secretary Robert Gates told a regional security conference in Singapore that clashes may erupt in the South China Sea unless nations with conflicting claims adopt a mechanism to settle disputes peacefully.

"There are increasing concerns. I think we should not lose any time in trying to strengthen these mechanisms that I've been talking about for dealing with competing claims in the South China Sea," he said.

"I fear that without rules of the road, without agreed approaches to deal with these problems, that there will be clashes. I think that serves nobody's interests," Gates added.

Speaking at the same conference Friday, Malaysian Prime Minister Najib Razak called for restraint in the South China Sea.