Days have passed since two incidents involving Chinese and Filipino vessels colliding in the disputed waters.
Reiterating his "ironclad" defense pledge to the Philippines was Mr. Biden.
Manila has removed floating obstacles and invited reporters to film what it considers to be Beijing's risky maritime maneuvers in an effort to refute Chinese claims to the waterways.
"Let me be absolutely clear: The United States has an unwavering commitment to defense against the Philippines. "The defense deal between the United States and the Philippines is unbreakable," he declared.
The US and its former colony, the Philippines, are required by the 1951 Mutual Defense Treaty to defend one another in the case of an armed assault.
"We will utilize our Mutual Defense Treaty with the Philippines for any attack on Filipino planes, vessels, or armed troops," he continued during his Wednesday speech at the White House, where he also greeted Australian Prime Minister Anthony Albanese.
The US had "no authority to become involved in a situation between China and the Philippines," according to Mao Ning, a spokesman for the Chinese foreign ministry.
In response to a query on the comment, she told reporters that if the US decides to defend the Philippines, its measures "must not affect China's sovereignty and maritime interests in the South China Sea."
China's "dangerous manoeuvres," according to the Philippines, caused a collision on Sunday between a Chinese coast guard ship and a Filipino supply boat in a region that is inside the country's Exclusive Economic Zone (EEZ). Manila reported that a Chinese militia boat "bumped" a Philippine coast guard vessel in a different incident.
The Filipino vessels were en route to Manila, which has grounded a dilapidated navy frigate in the Second Thomas Shoal in order to bolster its claims.
Gilberto Teodoro Jr., the defense minister of the Philippines, charged China with "distorting the tale to serve its own goals" and stated that the Chinese boats "deliberately hit" the Philippine vessels.
Mr. Biden reiterated these accusations, stating that at the time of the crashes, the Chinese vessels had "behaved dangerously and unlawfully."
Due to its proximity to Taiwan and the South China Sea, two possible Pacific flashpoints, the Philippines is a crucial strategic partner of the United States.
The Philippine government has stepped up its efforts to challenge China's actions in the South China Sea since President Ferdinand Marcos Jr. took office in June 2022 and restored the country's relationship with the United States.
The pro-China stance of Rodrigo Duterte, Mr. Marcos' predecessor, who came under fire for not doing enough to thwart Beijing's actions in the South China Sea, is reversed under Mr. Marcos' foreign policy.
Duterte declined to cite Manila's legal triumph over China in an international tribunal, which declared Beijing's expansive claims to nearly the whole South China Sea to be erroneous.