The Chinese vessels "took necessary control measures", the coastguard added, without going into details. There was no immediate comment from Japan.

China urged Japan to immediately cease all "illegal activities" in the area and ensure that similar incidents do not recur, the coastguard added.

The waters around Diaoyu Islands, which Japan calls the Senkaku Islands, are disputed and claimed by both China and Japan. The two sides have faced off in the waters, deploying patrol boats and urging the other to leave the area.

(Reporting by Beijing newsroom; Editing by Andrew Heavens)