The Japanese coast guard said the incursion into the waters of the uninhabited islands in the East China Sea -- which China also claims, referring to them as the Diaoyu Islands -- was the first since last Tuesday, Kyodo News reported.
Tensions have been rising between the two countries over their territorial claims, triggering widespread and violent protests across Chinese cities.
China's state-run Xinhua News Agency, quoting the Chinese State Oceanic Administration, said two of its marine surveillance ships "continued patrol and law enforcement activities around the Diaoyu Islands on Monday," adding "Japan recently provoked a dispute regarding the islands by severely infringing on China's territorial sovereignty."
The Japanese government earlier this month announced the purchase of the islands and bringing them under state control, which set of the protests in China.
The Kyodo report said while bilateral relations were deteriorating, there were no signs the dispute would be settled any time soon.
The Japanese government already has set up a special task force in the office of Prime Minister Yoshihiko Noda, who reportedly had instructed Japan's Vice Foreign Minister Chikao Kawai to ensure government officials "work closely together and collect information," Kyodo reported.
Japan's Chief Cabinet Secretary Osamu Fujimura told a news conference that the government was "strongly protesting" Monday's intrusions and urging the Chinese vessels to "exit from the territorial waters promptly."
The latest events have also led to the cancellation of ceremonial events that had been slated for Thursday in Beijing to mark the 40th anniversary of the normalization of ties between the two countries.
Separately, Kyodo reported the government had decided to send Kawai to China to seek ways to lessen the tensions.
Xinhua said the patrol by its ships was to exercise the administrative jurisdiction over the islands and its surrounding waters by conducting the patrol.
Separately, the China Daily, quoting analysts, said Monday the cancellation of the events marking the 40th anniversary of Sino-Japanese relations was a "a strong signal" that Beijing is adopting a tougher stance.
"China should be tough on the territorial issue," Feng Wei, a specialist on Japanese studies at Fudan University in Shanghai, told China Daily. "China should take this opportunity to push Japan back to the negotiating table."
Wang Ping, an expert on Japanese studies with the Chinese Academy of Social Sciences, said it is not a good time to celebrate the anniversary of bilateral relations.
"We have not seen any sincerity by the Japanese government to improve ties," Wang said.
China plans to use unmanned aerial vehicles to strengthen maritime surveillance over island waters, Xinhua had reported Sunday.
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