US President Joe Biden has warned China that the US will defend the Philippines in case of any attack in the disputed South China Sea.

The comments come days after two collisions between Filipino and Chinese vessels in the contested waters.

Mr Biden reiterated his "ironclad" defence commitment to the Philippines.

Manila has contested Chinese claims to the waters, cutting floating barriers and inviting media to film what it calls Beijing's dangerous moves at sea.

Mr Biden's statement on the South China Sea on Wednesday was his strongest since tensions between Beijing and Manila heated up in recent months.

"I want to be clear — I want to be very clear: The United States' defence commitment to the Philippines is ironclad. The United States defence agreement with the Philippines is ironclad," he said.

Signed in 1951, the Mutual Defense Treaty binds the US and the Philippines, its former colony, into defending each other in the event of an armed attack.

"Any attack on the Filipino aircraft, vessels, or armed forces will invoke our Mutual Defense Treaty with the Philippines," he added in his speech an the White House on Wednesday, as he welcomed Australian Prime Minister Anthony Albanese.

Chinese foreign ministry spokesperson Mao Ning said the US had "no right to get involved in a problem between China and the Philippines".

Should the US defend the Philippines, its actions "must not hurt China's sovereignty and maritime interests in the South China Sea", she told reporters in response to a question on the statement.

On Sunday, the Philippines said China's "dangerous manoeuvres" had led to a collision between a China coast guard ship and a Filipino supply boat in an area that falls inside the Philippines' Exclusive Economic Zone (EEZ). In a separate incident, Manila said a Chinese militia boat "bumped" a Philippine coast guard vessel.

The Filipino boats were on their way to a crumbling navy warship that Manila has marooned at the Second Thomas Shoal to reinforce its claims.

The Philippines' defence minister, Gilberto Teodoro Jr, said the Chinese boats "intentionally hit" the Philippine vessels and accused China of "distorting the story to fit its own ends".

Mr Biden echoed these claims, saying the Chinese vessels had "acted dangerously and unlawfully" when the collisions happened.

The Philippines is an important strategic ally of the US as it borders two potential flashpoints in the Pacific - the South China Sea and Taiwan.

Since President Ferdinand Marcos Jr took office in June 2022 and revived the Philippines' alliance with the US, Filipino authorities have become more aggressive in contesting China's actions in the South China Sea.

Mr Marcos' foreign policy is a reversal of the pro-China stand taken by his predecessor, Rodrigo Duterte, who was criticised for not doing enough to counter Beijing's aggression in the South China Sea.

Duterte refused to invoke Manila's legal victory against China in an international tribunal, that said Beijing's vast claims to almost the entire South China Sea is unfounded.