Chinese coast guard sailors brandishing knives, an axe and other weapons clashed 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, the Sierra Madre, deliberately grounded atop the disputed Second Thomas Shoal, Manila said.

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.

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

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

A Filipino sailor lost a thumb in the incident, which saw the Chinese coast guard confiscate or destroy Philippine equipment including guns, according to the Philippine military.

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.

Beijing has insisted that its coast guard behaved in a "professional and restrained" way during the confrontation 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 be clearly seen waving an axe.

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

"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, clad in 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.

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

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

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

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

The US has said that "an armed attack" against Philippine public vessels, aircraft, armed forces and coastguard anywhere in the South China Sea would invoke a mutual defense treaty between the two countries.

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

They also "underscored the United States' ironclad commitments to the Philippines under our Mutual Defence Treaty", Blinken said.

And one analyst told AFP this week's clashes "brought us perilously close" to a situation in which that treaty would be invoked.

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

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

(With Inputs From International Agencies)