The Philippines says Chinese coast guards fired water cannons and “overturned” a government ship in the South China Sea.
The incident occurred near the disputed Scarborough Reef and Beijing said it acted “in accordance with the law”.
The US ambassador to the Philippines has condemned China's “illegal use of water cannons and dangerous maneuvers”.
The South China Sea is at the center of a territorial dispute between China, the Philippines and other countries. But tensions between Manila and Beijing have sharply intensified over the past year.
On Wednesday, Manila released a video showing a Chinese coast guard vessel spraying water on a Philippine Department of Fisheries vessel.
Separate footage, apparently taken from the Philippine ship, showed its crew shouting “Collision! Collision!” while the Chinese boat crashes there.
The BBC has not independently verified the footage.
The Philippine Coast Guard said the Chinese Coast Guard vessel “intentionally side-swiped” the vessel and then “launched a second water cannon attack on the same vessel.”
The Chinese coast guard said in an initial statement that the Philippine vessels “came dangerously close” and that their crew's actions had been “in accordance with the law.”
He then accused the Philippines of making “false accusations in an attempt to mislead international understanding” and said he had deliberately collided with the Chinese ship.
But MaryKay Carlson, the U.S. ambassador to the Philippines, said “we condemn these actions” by China.
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It is the latest in a series of dangerous encounters over the past year as both sides seek to assert their claims to controversial reefs and outcrops in the South China Sea, including the Second Thomas Shoal and the Scarborough Shoal.
Collisions usually result from a game of cat and mouse in which boats try to chase the other side.
China has increasingly used powerful water cannons and lasers on Philippine ships, with Filipinos also accusing the Chinese of boarding their boats, leading to scuffles, as well as confiscating items and drilling into their inflatable boats.
