China's Xinhua news agency said in the morning that two civilian surveillance ships were undertaking a "rights defence" patrol near the islands, citing the State Oceanic Administration, which controls the ships. Two fishery patrol vessels were also detected inside waters claimed by Japan.
Japan lodged an official protest.
By afternoon, all four Chinese vessels had moved further away, the Japanese Coast Guard said.
Sino-Japanese relations deteriorated sharply after Japan bought the islands, called Senkaku in Japan and Diaoyu in China, earlier this month, sparking anti-Japan protests across China.
"In recent days, Japan has constantly provoked incidents concerning the Diaoyu islands issue, gravely violating China's territorial sovereignty," Xinhua reported.
The ship patrols were intended to exercise China's "administrative jurisdiction" over the islands, it said.
"Following the relevant laws of the People's Republic of China, (the ships) again carried out a regular rights defence patrol in our territorial waters around the Diaoyu islands."
Sino-Japanese ties have long been plagued by China's memories of Japan's military aggression in the 1930s and 1940s and present rivalry over regional influence and resources.
Japanese Vice Foreign Minister Chikao Kawai will visit China on Monday to discuss Sino-Japanese relations with Chinese Vice Foreign Minister Zhang Zhijun, the Foreign Ministry said.
|May 22||Cops crack down on porn films targeting lolicon lechers|
|With crackdowns on violators of child prostitution and pornography statutes having increased in recent years, Nikkan Gendai (May 17) wonders how a manager of an online operation that primarily sold lolicon (“Lolita complex”) films was able to evade detection for an extended period prior to his arrest earlier this month. (Tokyo Reporter)|
|May 22||X Japan waxes lyrical at Madame Tussauds debut|
|This Monday, members of the seminal metal band X Japan were in Odaiba rubbing shoulders with the likes of Brad Pitt, Lady Gaga and AKB48′s Yuko Oshima. The catch? They were all made out of wax. (Japan Times )|
|May 22||Transport ministry to unify rules for baby strollers on buses, trains|
|The Ministry of Land, Infrastructure, Transport and Tourism has announced that it intends to draw up a set of unified rules for the use of baby strollers on buses and trains. (Japan Today )|
|May 21||Japan Crown Prince to visit Spain|
|Japanese Crown Prince Naruhito will visit Spain for seven days from June 10, the government said Tuesday. (Jiji Press )|
|May 21||Tokyo broker for Thai hostesses busted for wrongful employment|
|Tokyo Metropolitan Police on Monday announced the arrest of a broker of Thai females for violating immigration laws by employing the women as masseuses. (Tokyo Reporter )|
|May 21||Claim filed against Yamaguchi-gumi top bosses for arson death in Nagoya|
|The parents of a nightclub worker killed in an arson fire three years ago filed a suit in the Nagoya District Court on Monday seeking damages against top members of the Yamaguchi-gumi organized crime group. (Tokyo Reporter )|
|May 21||Senior Kyodo News official dismissed over improper act|
|Kyodo News said Monday that it has dismissed Satoshi Kondo, 51, deputy chief of its general administration bureau and former personnel affairs division chief, for meeting individually with a female student searching for a job and doing an inappropriate act. (Jiji Press )|
|May 20||Saitama cops bust massive child porn DVD operation|
|Saitama and Okayama prefectural police last week arrested the manager of an online porn DVD operation that specialized in films featuring children. (Tokyo Reporter)|
|May 19||Japan's child kidnapping problem|
|Dozens of American children are abducted to Japan every year-not by strangers, but by parents after messy divorces. (thedailybeast.com )|
|May 18||5-year-old boy's hand gets caught in shopping mall escalator|
|A 5-year-old boy sustained an injury at a shopping mall in Nagoya on Friday after his hand became trapped in an escalator. (Japan Today )|