"According to our data, the Chinese coastal patrol ships carried out routine patrols near the Diaoyudao Islands when they discovered the illegal operation of a Japanese ship. Chinese ships tracked the Japanese vessel in accordance with the law and urged it to leave the waters. China made a representation to Japan through diplomatic channels, urging them to stop unlawful actions," Zhao said.
The diplomat added that the islands were part of China and thus it had every right to maintain law and order in its waters.
The Kyodo news agency reported on Saturday, citing sources, that the Japanese Foreign Ministry had filed a diplomatic protest against China to the Chinese Embassy by phone over violations of its maritime border by Chinese patrol vessels.
On Friday, four Chinese patrol ships one by one entered the Japanese waters, with two of them trying to pursue a fishing vessel there. A similar incident took place earlier that day when four patrol ships emerged near the border, with two of them crossing into the Japanese territory.
The islands in question have been an object of territorial disputes between Tokyo and Beijing for a long time. Japan maintains it has them since 1895. China, in turn, has been claiming that the islands are marked as a Chinese territory on Japanese maps circa 1783 and 1785.
Following World War II, the islands were controlled by the United States and handed over to Japan in 1972. Both Taiwan and mainland China claim that Japan has been illegally seizing them while Tokyo rebuts that they have begun claiming the islands for themselves after in the 1970s the surrounding water area was found to be full of valuable minerals.
The tensions have exacerbated after the Japanese government bought three of the islands from a private owner in 2012.