Japan said a Chinese government ship briefly entered its territorial waters off disputed islands on Saturday, as the Japanese premier vowed he would not tolerate Beijing's incursions into the area.
The fisheries patrol boat entered the waters in the East China Sea at 4:48 pm (0748 GMT) and was sailing some 19 kilometres northwest of Uotsuri, one of the Senkaku islands, Japan's coastguard said in a statement.
But the Chinese ship moved out of the zone after about an hour, watched by a Japanese coastguard vessel, it said.
Beijing claims the Japanese-controlled islands, which it calls the Diaoyus.
The incident was the latest in a series, with Japan claiming in one case that Chinese vessels had locked weapons-targeting radar onto a ship and a helicopter. Beijing denied the charge.
Saturday's incident came as Prime Minister Shinzo Abe, now on his first visit to the United States since he took office late December, vowed that he would not tolerate any challenge to control over the contested islands.
"We simply cannot tolerate any challenge now and in the future. No nation should make any miscalculation or underestimate the firmness of our resolve," Abe said Friday in Washington.
Speaking after talks with President Barack Obama at the White House, however, Abe cautioned that "I have absolutely no intention to climb up the escalation ladder".
The dispute between Asia's two largest economies intensified in September when Tokyo nationalised three islands in the chain, in what it said was a mere administrative change of ownership.