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.

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 incident marks the second confrontation this week between Manila and Beijing over disputed South China Sea islands.