Three Chinese government ships entered waters around islands at the centre of a dispute with Tokyo on Monday, the day after China rebuked the United States for comments seen as supporting Japan.
Japan's coastguard said the maritime surveillance boats were sailing in and out of waters around a chain of Tokyo-controlled islands known as the Senkakus in Japan, which Beijing calls the Diaoyus, for nearly nine hours.
The three boats all left the waters by 3:45 pm (0645 GMT) and were sailing away from the islands, the coastguard said.
China has repeatedly sent ships to the area since Japan nationalised some of the chain in September, a move that triggered a diplomatic dispute and huge anti-Japan demonstrations across China.
Beijing has also sent air patrols to the archipelago in the East China Sea, and in recent weeks both Beijing and Tokyo have scrambled fighter jets, though there have been no clashes.
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