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.

China's activity in the contested South China Sea is "hindering" Filipino companies from exploring natural resources in the region, Philippines Foreign Secretary Enrique Manalo said during a talk at Chatham House in London on Tuesday.

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.

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.

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.”

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.

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.