Blinken was in Manila with US Defense Secretary Lloyd Austin as part of an Asia-Pacific tour to strengthen Washington's latticework of alliances aimed at countering Beijing.

"We're now allocating an additional $500 million in foreign military financing to the Philippines to boost security collaboration with our oldest treaty ally in this region," Blinken told a joint news conference.

Blinken described it as a "once in a generation investment" to help modernise the Philippine armed forces and coast guard.

Blinken and Austin met with President Ferdinand Marcos, who has taken a strong stand against Chinese actions in the South China Sea, before holding "2+2" talks with their Philippine counterparts Enrique Manalo and Gilberto Teodoro.

The latest high-level US visit follows a series of escalating confrontations between Philippine and Chinese vessels in the disputed waterway that have raised concern that Washington could be dragged into a conflict due to its mutual defence treaty with Manila.

The additional funding is part of the $2 billion in foreign military financing approved by the United States in April.

It comes as the Philippine modernises its armed forces, one of the weakest in Asia, and bolsters its coast guard.

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 in the region.

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.

There has been a revolving door of top US officials passing through the Philippines since Marcos took office in 2022 and adopted a more US-friendly foreign policy.

Marcos expanded an agreement giving American troops access to nine Philippine military bases, including in the far north of the country, which has infuriated Chinese leaders.

The agreement allows US troops to rotate through the bases and also store defence equipment and supplies at them.

Marcos told Austin and Blinken on Tuesday that he was "very happy" about the open lines of communication with the United States, which helped Manila be "agile in terms of our responses" on issues including the South China Sea.

Blinken and his Chinese counterpart Wang Yi sparred on Saturday over the South China Sea when they met on the sidelines of the foreign ministers meeting of the Association of Southeast Asian Nations in Laos.

Wang told Blinken the United States should "refrain from fanning the flames, stirring up trouble and undermining stability at sea," according to a foreign ministry statement.

"The risks and challenges facing China-US relations are still rising," he said.