Four Chinese coastguard vessels have stayed in the area in the past several days, with three of them sailing into the territorial waters shortly after 5pm on Saturday, the Japanese coastguard said.
It was the latest in a series of incursions by Chinese government ships in recent months around the Senkaku islands, which Beijing claims as the Diaoyus.
The dispute has been cited as a potential flashpoint that may even lead to armed conflict between the Asian giants.
All the ships left the 12-nautical-mile band of waters by 11pm, with three sailing into the contiguous zone, the agency said.
Contiguous waters are defined as a maritime zone adjacent to a country's territorial sea where a coastal state may exercise controls necessary to prevent and punish infringement of its laws.
The Japanese coastguard also said its vessels spotted a small yacht believed to be of British registry raising the Chinese flag some 50 kilometres northwest of one of the islands and later entering territorial waters shortly after 5pm on Saturday.
Sailors of the yacht then threw a buoy with what the agency described as a red flag into the water and left the area, it said.


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