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.

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.