Japan is threatening China militarily which is "completely unacceptable", Chinese Foreign Minister Wang Yi told his German counterpart, after Japan said that Chinese fighter jets had aimed their radar at Japanese military aircraft.

As relations with China continue to deteriorate, Japan is embarking on its biggest military buildup in at least four decades.

China operates the world’s largest navy by hull count, allowing it to expand its military presence and assert its influence.

China has denied that its military aircraft locked radar onto Japanese Air Self-Defense Force fighter jets on Saturday. It says Japan obstructed a training drill.

Taiwan and Japan voiced concern on Friday over Chinese military activities in the region, after Reuters reported that Beijing had deployed a large number of vessels across East Asian waters this week in its largest maritime show of force to date.

These ships fit into China’s strategy of extending its defensive perimeter beyond Japan, Okinawa, Taiwan, the Philippines, and Indonesia.