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.

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

China’s military said it drove away three Philippines aircraft “illegally” flying over the disputed Spratly Islands, marking the second aerial incident this week involving Beijing and Manila in the South China Sea.

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.”

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.