Chinese government ships entered territorial waters off disputed Tokyo-controlled islands for the second straight day Wednesday, Japanese coastguards said.
Three maritime surveillance ships "ignored warnings from patrol vessels of our agency... and entered our country's territorial waters" shortly after 12:30 pm (0330 GMT), the coastguard said in a statement.
"The (Chinese vessels) responded by saying 'You are already inside Chinese territorial waters. Do not interfere with our operations and leave these waters,'" the Japanese agency said.
The three Chinese ships, which were off Kubashima, one of the islands in a chain known as the Senkakus in Japan and the Diaoyus in China, left the immediate area soon after 3:00 pm, the Japanese coastguard said.
The Chinese ships were among four vessels that had been in island waters on Tuesday, remaining for around six hours, despite demands from Japan that they leave.
The Japanese government lodged protests to China over the incidents.
Tensions have risen in recent months over the islands, which lie in rich fishing grounds and on key shipping lanes in the East China Sea. The seabed in the area is also believed to harbour mineral reserves.
Diplomats from China and Japan traded insults at the United Nations in New York last week and sometimes violent demonstrations in Chinese cities hit Japanese business interests last month.
International Monetary Fund chief Christine Lagarde, in an interview published Wednesday, voiced concerns over the spat, warning the shaky world economy could not afford for the two economic powers to be so distracted.