Two China Coast Guard vessels, one of which is equipped with what the Japan Coast Guard said were guns, briefly entered Japanese territorial waters around the disputed Senkaku Islands in the East China Sea on Friday.

The intrusion occurred at around 2:20 p.m. and the ships left the waters about 100 minutes later, according to the Japan Coast Guard.

Chinese vessels were last found sailing in Japanese territorial waters near the Senkakus on Dec. 26.

When a Japan Coast Guard patrol ship warned the Haijing 2401 and the Haijing 31241, the vessel believed to be armed, the they replied that the Japanese ship had entered Chinese territorial waters and asked it to leave, according to the 11th Regional Coast Guard Headquarters in Naha, Okinawa Prefecture.

Separately, a Chinese marine research ship was spotted within Japan's exclusive economic zone about 415 km southeast of Okinawa's main island. It marked the fourth straight day that a Chinese survey ship was found operating in the area.

China and Taiwan claim the Senkaku Islands, calling them Diaoyu and Tiaoyutai, respectively. China stepped up its claim to the islets after Japan purchased three of the islands from a Japanese individual and put them under state control in 2012.