Four China Coast Guard vessels entered Japanese waters around the Senkaku Islands in the East China Sea on Thursday morning, the Japan Coast Guard said, adding that what appeared to be a drone was seen flying above them.

A high-ranking Foreign Ministry official lodged a protest with a senior diplomat at the Chinese Embassy in Tokyo, saying over the telephone that the flying of the drone-like object in Japanese territory near the Senkakus could unilaterally escalate the situation in the area, a ministry official said.

The Senkaku Islands are claimed by China and Taiwan, which call them Diaoyu and Tiaoyutai, respectively.

The Chinese vessels entered Japanese territorial waters shortly after 10 a.m. and one of them appeared to be armed, the Japan Coast Guard said.

The Japan Coast Guard ordered the Chinese ships to leave the waters, and they complied after loitering for nearly two hours. The apparent drone was seen at around 10:50 a.m., the first time such an object has been observed in the area, according to the Japan Coast Guard.

The Senkaku Islands are a group of Japan-administered uninhabited islets between Okinawa and Taiwan. They are administratively part of the city of Ishigaki in Okinawa.

Chinese government vessels last entered waters in the area on May 8.