Six Chinese surveillance ships entered waters near disputed islands claimed by Tokyo and Beijing today, raising tensions between Asia's two biggest economies to their highest level since 2010 over a long-running territorial row.
Japan protested to China and urged that the situation not be allowed to escalate.
Diplomats say Tokyo and Beijing would prefer to keep the row from spiralling out of control, but with China facing a once-in-a-decade leadership change, an election looming in Japan and mutual mistrust deep, managing the feud could be difficult.
China's foreign ministry said that the ships entered the disputed waters to conduct maritime surveillance and that for the first time China was carrying out a mission of "law enforcement over its maritime rights".
"It reflects our government's jurisdiction over the Diaoyu islands," it said in a statement. The ministry has used similar language in the past.
The coast guard said it ordered the Chinese ships to leave the area, but only three complied. No force had been used to expel the Chinese ships, a coast guard official said. Chinese state television showed pictures of an official onboard a Chinese ship radioing a warning to Japanese ships around the island to withdraw from China's islands.
"We lodged a strong protest and also we made a strong case that the Chinese side should leave from the territorial waters around the Senkaku islands," Japanese foreign minister Koichiro Gemba told a news conference in Sydney, Australia after talks with Australia's foreign and defence ministers.
"I'd like to underscore that we should never let the situation escalate and we have strong hopes for the Chinese to respond in an appropriate and calm manner," added Mr Gemba, who said he would return to Tokyo a day earlier than planned.
Chinese ambassador Chen Yonghua, who was summoned to Japan's foreign ministry, repeated China's stance on the islands but added Beijing also hoped the situation would not escalate or hurt broader ties, a Japanese foreign ministry statement said.
The islands, known as Senkaku in Japanese and Diaoyu in Chinese, are near potentially huge maritime gas and oil fields.
The uninhabited islets were at the centre of a chill between Beijing and Tokyo in 2010, after Japan arrested a Chinese trawler captain whose boat collided with Japanese Coast Guard vessels near the area.
Reuters