A series of escalating confrontations between Philippine and Chinese vessels in the disputed waterway have raised concern that Washington could be dragged into a conflict due to its mutual defence treaty with Manila.

US Secretary of State Antony Blinken and Defence Secretary Lloyd Austin are in Asia to strengthen a latticework of regional alliances as Washington counters China's growing military and diplomatic influence.

Blinken and Austin kicked off their Manila leg with a meeting with President Ferdinand Marcos, before holding "2+2" talks with their Philippine counterparts Enrique Manalo and Gilberto Teodoro.

It marks the first time the Philippines has hosted the "2+2" talks, which Blinken said were evidence of "a steady drum beat, a very high level of engagements between our countries".

"We are truly grateful for this partnership," Blinken told Marcos at the presidential palace.

The Philippines' proximity to the hotly contested South China Sea, as well as self-ruled Taiwan, would make it a key partner for the United States if a conflict were to break out.

Beijing claims almost the entire waterway, despite an international ruling that its assertion has no legal basis, and considers democratic Taiwan to be part of its territory.

Under their mutual defence treaty, the Philippines and the United States are required to come to the other's defence in case of an "armed attack" against vessels, aircraft, military and coast guard anywhere in the Pacific theatre, which Washington says includes the South China Sea.

Beijing's actions in the strategic waterway have been high on the agenda for Blinken's Asia-Pacific trip, which has included the foreign ministers meeting of the Association of Southeast Asian Nations in Laos and "2+2" talks in Japan.

A Filipino sailor lost a thumb in a June 17 confrontation near the flashpoint Second Thomas Shoal in the Spratly Islands.

Chinese coast guard members wielding knives, sticks and an axe foiled a Philippine Navy attempt to resupply Filipino troops stationed on a crumbling ship.

The two sides subsequently agreed to a "provisional arrangement" for the delivery of food and water to the Sierra Madre, which was deliberately grounded in 1999 to assert Manila's claims to the area.

The Philippines said it had carried out a resupply mission on Saturday without "untoward incident".