President Ferdinand Marcos said Thursday that the Philippines needs to do more than protest Beijing's "illegal actions" in the South China Sea.

Chinese coast guard personnel wielding knives, sticks and an axe surrounded and boarded three Filipino navy boats last week, video showed, foiling what Manila said was a resupply mission to troops manning a grounded warship on Second Thomas Shoal.

It was the latest and most serious incident in a series of escalating confrontations between Chinese and Philippine ships as Beijing steps up efforts to push its claims to nearly all of the strategically located waterway.

"We have filed over a hundred protests, we have already made a similar number of demarches," Marcos told reporters. 

"We have to do more than just that," he said, without specifying what other steps Manila might take.

The clashes have raised concern the conflict will draw in the United States, which is bound by a 1951 mutual defence pact to come to Manila's aid in case of an "armed attack" on its forces or vessels in the Pacific theatre.

Manila has also raised concerns that Chinese forces might take action against the warship BRP Sierra Madre, an ageing ship that was deliberately grounded on the shoal in 1999 to assert Philippine claims to the area.

A small garrison of Filipino marines stationed aboard the decrepit vessel relies on frequent resupply for survival.

Marcos on Thursday echoed his senior security aides' assessment that the 17 June clash next to the grounded warship did not constitute an armed attack.

"It's not armed. There was no gunshot. They did not point a gun at us, but it was a deliberate action to stop our people," Marcos said.

"So, although there were no arms involved, nonetheless, it is still a deliberate action and it is essentially an illegal action that was taken by Chinese forces."

A Filipino soldier lost a finger in the incident, with Manila also accusing the Chinese coast guard of stealing guns and damaging three boats along with navigational and communication equipment.

Beijing insisted its coast guard behaved in a "professional and restrained" way and blamed Manila for the clash.

Philippine Foreign Secretary Enrique Manalo said Wednesday that Manila had filed a diplomatic protest.

On Tuesday, Manalo told a Senate hearing that Manila hopes to convene a meeting with Beijing early next month "specifically to discuss the recent incidents".

Second Thomas Shoal lies about 200 kilometers (120 miles) from the western Philippine island of Palawan and more than 1,000 kilometers from China's nearest major landmass, Hainan island.

China deploys coast guard and other boats to patrol the waters around the shoal and has turned several reefs into artificial militarized islands.