Seven Chinese warships, including two destroyers, were sighted on Tuesday in waters off a Japanese island, according to the defence ministry, as tension mounted between the two Asian giants over territorial disputes.
The naval ships passed the contiguous zone, a band of water just outside Japan's territorial waters, which are governed by international maritime law.
The sighting comes at a time when Japan and China are already at loggerheads over a disputed archipelago in East China Sea.
The seven ships were spotted sailing at around 7 am, nearly 49 km south-southeast of Yonaguni Island in Okinawa Prefecture, the ministry was quoted as saying by Japanese news agency Kyodo.
Yonaguni is an inhabited territory which has been internationally acknowledged as Japanese. The ships spotted included two destroyers, at least one of which had missile capacity, two frigates, two submarine rescue ships and one supply ship, the ministry said.
There has been a long standing dispute between Japan and China over the Senkaku islands, which are administered by Japan but are claimed by China.
Both China and Japan have been strengthening their naval muscle in the area around Okinawa in light of the dispute but have restrained from any clashes between their warships.