Chinese coast guard sailors brandished knives, an axe and other weapons in a clash with Philippine naval vessels near a strategic reef in the South China Sea, dramatic new footage released by Manila showed.

The clash took place Monday as Philippine forces attempted to resupply marines stationed on a derelict warship that was deliberately grounded atop the disputed Second Thomas Shoal in 1999 to assert Manila's territorial claims.

It was the latest in a series of escalating confrontations between Chinese and Philippine ships in recent months as Beijing steps up efforts to push its claims to the disputed area.

Philippine military chief General Romeo Brawner said the "outnumbered" Filipino crew had been unarmed and had fought with their "bare hands".

A Filipino sailor lost a thumb in the clash, in which the Chinese coast guard confiscated or destroyed Philippine equipment including guns, according to the Philippine military.

Fresh footage released by the Philippine military late Wednesday showed small boats crewed by Chinese sailors shouting, waving knives and using sticks to hit an inflatable boat as a siren blares.

A voice speaking Tagalog can be heard in one clip saying someone had "lost a finger".

Manila's footage of the clash stands in stark contrast to photos released by Beijing's state media on Wednesday, which did not show Chinese forces wielding weapons.

'Violent confrontation'

Asked about the videos on Thursday, Chinese foreign ministry spokesman Lin Jian said Manila's comments on the clash were "totally bogus accusations that confuse black with white".

He blamed the Philippines for the confrontation, saying they had "escalated tensions" and accused them of ramming Chinese boats. 

Lin said the Philippine boats had been trying "to sneak in building materials, but also tried to smuggle in military equipment".

Beijing has insisted that its coast guard behaved in a "professional and restrained" way and claimed "no direct measures" were taken against Filipino personnel.

But in a clip shared by Manila, a Chinese sailor standing on the deck of one of the boats can clearly be seen waving an axe.

Another shows a Chinese coast guard sailor striking the inflatable boat with a stick. A second man can also be seen stabbing the boat with a knife.

The Philippines military said an axe-wielding sailor had "threatened to injure" a Filipino soldier, while others were "explicitly threatening to harm" Filipino troops.

"The (Chinese coast guard) personnel then began hurling rocks and other objects at our personnel," Manila said.

"They also slashed the (inflatable boats), rendering them inoperable."

The Filipino sailors, wearing brown camouflage with helmets and vests, are not carrying weapons in the clips.

"Amidst this violent confrontation, the CCG (Chinese coast guard) also deployed tear gas, intensifying the chaos and confusion, while continuously blaring sirens to further disrupt communication," the caption said.

Manila has accused Beijing of an "act of piracy" against its forces.

It has also demanded the return of items "looted" by the Chinese side, including seven guns, and reparations for damaged equipment.

'Perilous' situation

Analysts say Beijing is escalating confrontations with the Philippines in a bid to push it out of the South China Sea.

Jay Batongbacal, director for the Institute for Maritime Affairs and Law of the Sea in Manila, told AFP that China's forces could be poised to seize the grounded Philippine warship, the Sierra Madre.

"The deployment of their forces at present around the Sierra Madre and then the many reefs around the Kalayaan island group is indicative that they're ready to do it," he said, referring to Manila-claimed areas in the Spratly Islands.

The United States has said that "an armed attack" against Philippine public vessels, aircraft, armed forces and coastguard anywhere in the South China Sea would require it to come to Manila's defence as a treaty ally.

US Secretary of State Antony Blinken "emphasized that (China's) actions undermine regional peace and stability" in a call with his Philippine counterpart Enrique A. Manalo on Wednesday, according to the State Department.

Blinken said they also "underscored the United States' ironclad commitments to the Philippines under our Mutual Defense Treaty".

Another analyst said the clashes "brought us perilously close" to a point where the United States would be required to intervene militarily.

"The Philippines will likely need to continue resupply missions to the Sierra Madre, one way or another," said Duan Dang, a Vietnam-based maritime security analyst.

"Backing down and accepting Beijing's terms regarding these operations would mean relinquishing sovereign rights within its Exclusive Economic Zone," he said.