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.

The Chinese helicopter was attempting to force a Cessna Caravan turboprop plane belonging to the Philippine Bureau of Fisheries and Aquatic Resources out of what China claims is its airspace over the hotly disputed Scarborough Shoal off the northwestern Philippines.

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.