Chinese President Hu Jintao said on Sunday that Japan should not make a "wrong decision" over the Diaoyu Islands during his brief meeting with Japanese Prime Minister Yoshihiko Noda after weeks of tension between the neighbors.
The two leaders met for 15 minutes on the sidelines of the Asia-Pacific Economic Cooperation summit in Vladivostok in Russia.
Hu told Noda that a "severe situation" had developed over the Diaoyu Islands in the East China Sea.
He raised objections to a plan by Noda's government to buy the islands from so-called private Japanese owners.
"It is illegal and invalid for Japan to buy the islands via any means. China firmly opposes it," Hu told Noda.
"China will unswervingly safeguard its sovereignty. Japan must realize the severity of the situation and not to make a wrong decision," the president said.
He urged Japan to work with the Chinese side to maintain the overall development of the two countries' relations.
Noda said Japan hoped to develop a mutually beneficial, strategic relationship with China and that he planned to deal with current relations from a "comprehensive perspective," Japan's Jiji news agency reported.
No talks had been scheduled during the APEC summit, but Noda said on Friday he would not shun a brief exchange.
Tension over the islands flared last month when Japan detained a group of Chinese activists who landed on one of them. That sparked anti-Japanese protests in several Chinese cities before Japan released the activists.