The disputed islands, known as the Senkaku islands in Japan and Diaoyu islands in China, in the East China Sea. (File photo)
Four Chinese government ships have sailed in waters around the disputed islands in the East China Sea, the Japanese coastguard says.
"Patrol ships from our agency have been telling them to sail outside of our territorial waters. There has not been any response" from the Chinese maritime surveillance ships, it said in statement on Tuesday.
The statement said that the ships entered the waters of the islands, known as Senkaku in Japan and Diaoyu in China, at 12:30 p.m. (0330 GMT) Tuesday.
Japan and China have long been competing over the sovereignty of the uninhabited islands, which would give the owner exclusive oil, mineral and fishing rights in surrounding waters.
Tensions heightened between Tokyo and Beijing after Japan signed a deal on September 11 to buy three of the islands from their private Japanese owners in line with plans to nationalize the archipelago.
The move sparked massive anti-Japan protests across China, forcing Japanese brand-name firms to close their businesses in the country after their offices and factories came under attack.