At least 47,000 personnel will take part in the biennial Keen Sword exercise, which runs until 16 November.
It is taking place off Okinawa, north of islands both Japan and China claim.
The two sides are locked in a diplomatic row over the islands, known as Senkaku in Japan and and Diaoyu in China.
Japan controls the islands, which Taiwan also claims. The Japanese government’s acquisition of three of the islands from their private Japanese owner in September sparked both diplomatic and public protests in China.