China Coast Guard (CCG) vessels 2502, 2166, 2101 and 33115 conducted a patrol in the country's territorial waters off the Diaoyu Islands on Friday, according to an online statement by China's State Oceanic Administration.
The Japanese media said it was the second day in a row that CCG vessels were found in the waters off the Diaoyu Islands.
The Chinese government has repeatedly stressed that the Diaoyu Islands and their affiliated islets are Chinese territory, but Japan also claims sovereignty over the islands.
According to Japanese daily Sankei Shimbun, Japan's 11th Regional Coast Guard Headquarters in Naha said it found four CCG vessels in its "territorial waters" near the Diaoyu Islands on Friday, adding that it was the second consecutive day that Chinese coast guard vessels appeared in the area. The Japanese authorities warned the Chinese vessels not to enter its territorial waters.
Beijing says Japan in no position to point fingers
Earlier this month, China expressed opposition to Japan's defense white paper for 2017, accusing Japan of making irresponsible remarks about China's marine activities.
In the white paper, Japan claimed that "China has tried to change the status quo in the East China Sea and South China Sea based on its own assertions, and this has become a common concern of the region and the world at large." It accused China of frequently encroaching into Japanese waters.
Chinese Foreign Ministry spokesman Geng Shuang said on August 9 that conducting patrol and law-enforcement activities in waters off the Diaoyu Islands is China's inherent right and Japan is in no position to point fingers at those activities.
The Chinese side, carrying out normal sea and air activities in accordance with international law, relevant domestic laws and regulations as well as national defense needs, is beyond reproach, he said.
On the same day, Chinese Defense Ministry Spokesman Wu Qian reaffirmed China's position that the Diaoyu Islands and their adjacent islets are Chinese territory, and that this is backed up by both history and legal proof.
He vowed that China would continue its activities in the disputed waters.