Japanese aircraft have spotted seven Chinese warships in waters off a southern Japan island and about 125 miles from the uninhabited isles at the centre of a territorial dispute between the two countries.

Japanese officials said the ships were sighted about 30 miles from the island of Yonaguni, in Japan's Okinawa prefecture.

The ships were believed to be returning to China after training in the Pacific.

Japan considers the area part of its contiguous waters, but it is not illegal for foreign vessels to transit them.

Defence Minister Satoshi Morimoto said Japan is monitoring the ships' movement.

China and Japan have stepped up their naval activities in the area around Okinawa because of the dispute, but there have been no clashes between their warships.