NAHA/BEIJING - Japan has lodged two protests to China after spotting an unprecedented 13 Chinese Coast Guard vessels, some of which were equipped with guns, in waters around disputed islands in the East China Sea, Kyodo news agency reported.

The number is a record since the Japanese government purchased most of the Senkaku islands, known as Diaoyu in Chinese, from a private owner in September 2012, the report said on Sunday (Aug 7).

The previous record of 12 was logged shortly after the purchase, which was bitterly protested by China at the time.

Seven of the vessels were spotted on Saturday, together with some 230 Chinese fishing boats.

Two more China Coast Guard ships entered Japanese territorial waters on Sunday morning, followed by four ships in the afternoon, Kyodo reported, citing the Japan Coast Guard.

The vessels sailed into contiguous waters, which countries can police for customs and immigration violations, despite Japan’s repeated protests over recent, smaller-scale entries.

Some Chinese Coast Guard vessels also entered what Japan considers its own waters, Japan’s government said according to Reuters.

Global Times, a nationalist Chinese newspaper, said on Monday (Aug 8)the move by Beijing was meant to "demonstrate China's sovereignty over the Diaoyu islands" as ties between China and Japan deteriorated recent months due to Japan's "meddling" in China's South China Sea disputes with South-east Asia nations.

"It's normal for China to send Coast Guard vessels to the Diaoyu area to safeguard China's fishing boats, as the Diaoyu Islands are an inherent part of Chinese territory," Lü Yaodong, director of the Institute of Japanese Studies at the Chinese Academy of Social Sciences, was quoted as saying by Global Times.

Japan will keep urging China not to escalate the situation in the East China Sea, while responding firmly and calmly, Japanese Chief Cabinet Secretary Yoshihide Suga was quoted by Reuters as saying on Monday.