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 South China Sea is an important shipping route that holds significant oil and gas reserves.

Disputed South China Sea airspace that Beijing claims as its own falls within Manila’s Exclusive Economic Zone, where the Philippines and other countries enjoy freedom of overflight.

The Philippines and Japan pledged to enhance their defense alliance through training exercises, logistical activities, equipment transfers and intelligence sharing on Monday amid China’s assertive moves in the South China Sea.

Maritime tensions between China and the Philippines were in the spotlight at the Munich Security Conference, with former Chinese Vice Foreign Minister Fu Ying calling the occupation of disputed features in the South China Sea “a red line.”

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.

While Russia's war against Ukraine and a wavering transatlantic alliance drew the world's attention at this year's Munich Security Conference, sparks also flew over claims in the Sea as debate involving participants representing Beijing and Manila dug into their positions in the region.