A Philippine plane warned a Chinese military helicopter over the South China Sea that it was "flying too close," as tension between the U.S. ally and Beijing soars.

A Chinese military helicopter flew within 10 feet (3 meters) of a Philippine patrol plane over the South China Sea on Tuesday, in what observers said was the second incident of potentially catastrophic behavior by the People’s Liberation Army against foreign aircraft in a week.

The United States condemned the "dangerous" manoeuvres of a Chinese navy helicopter that endangered the safety of a Philippine government aircraft patrolling a disputed shoal in the South China Sea, its ambassador to Manila said on Wednesday.