TOKYO - Six Chinese patrol ships entered Japanese waters near disputed islands claimed by both Beijing and Tokyo on Friday, said Japan's Coast Guard, further heightening tensions in a long-running territorial dispute between Asia's two biggest economies.
The coast guard ordered the ships to leave Japan's territorial waters, but only two complied, leaving four Chinese vessels still in Japanese waters, the coast guard said.
No force had been used to remove the Chinese ships, a coast guard official said.
"We'll do our utmost in vigilance and surveillance," said Prime Minister Yoshihiko Noda when asked about Japan's responses.
The islands, known as Senkaku in Japanese and Diaoyu in Chinese, are near potentially huge maritime gas and oil fields.
Tensions flared last month when Japan detained a group of Chinese activists who had landed on the islands and Japanese nationalists landed on the islands. Anti-Japanese protests rocked several Chinese cities.
Bilateral relations were frayed further on Tuesday when Japan, which controls the islands, said it had bought them from a private owner, ignoring warnings from China.
China warned Japan on Thursday that trade could be hurt by the flare-up in tension. A Nissan Motor Co Ltd 7201.T executive has said the tensions were affecting business with China.
The tensions with Japan come while China's ruling Communist Party is preoccupied with a forthcoming once-in-a-decade leadership change, as well as slowing economic growth.
The United States this week urged both sides to tone down increasingly impassioned exchanges over the longstanding row.
The last time Chinese government-affiliated ships entered Japanese territorial waters near the disputed islands was in July, the coast guard said. That incident ended peacefully.