Three Chinese ships sailed through disputed waters off Tokyo-controlled islands in the East China Sea on Monday, the latest such incident in the bitter territorial row between the Asian giants.
The Chinese coastguard vessels entered the 12-nautical-mile territorial waters off one of the Senkakus, which China claims and calls the Diaoyus, at around 10:00 am (0100 GMT), Japan's coastguard said.
Chinese vessels and aircraft have regularly approached the East China Sea archipelago -- thought to harbour vast natural resources belows its seabed -- after Japan nationalised some of the islands in September 2012, setting off the latest round in a long-running territorial dispute between the Asian powers.
The incident comes just days after US Secretary of State John Kerry raised concerns about China's territorial ambitions during talks with senior Chinese leaders including President Xi Jinping and Premier Li Keqiang in Beijing.
Fears of conflict rose in November when China imposed an air defence identification zone (ADIZ) over the East China Sea and said it required notification from planes crossing the area.
Washington was angered by the move, saying it could lead to confusion high in the skies.
On Friday Kerry warned Beijing against unilateral moves to set up a similar air defence zone over the South China Sea, where the Philippines in particular has voiced worries about China's maritime claims.
Earlier this month, the top US diplomat had vowed that the United States would defend Japan against attack including over the disputed islands in the East China Sea.