The Xiang Yang Hong 18, a Chinese research vessel, steams through Japan's exclusive economic zone, Wednesday, Oct. 18, 2023. (Japan coast guard)

Tokyo lodged diplomatic protests with Beijing this week after a Chinese research vessel was spotted in its exclusive economic zone near disputed islets in the East China Sea.

The ship, Xiang Yang Hong 18, was found just after 8 a.m. Wednesday by a Japan coast guard patrol boat about 80 miles northeast of Taisho Island, one of the Senkakus, a coast guard spokesman said by phone Thursday.

It appeared to be conducting a survey and had extended a wire-like object from its stern underwater, he said.

Foreign vessels are free to pass through a country’s exclusive economic zone but permission is required to conduct maritime research, according to the U.N. Convention on the Law of the Sea.

“It is unacceptable to implement research activities without Japan’s consent,” the same spokesman said in an emailed statement Thursday. Some government officials in Japan speak to the media on condition of anonymity as a requirement of their employment.

After the ship was spotted, Japan’s coast guard demanded the crew to cease and desist by radio, the spokesman said. Its crew initially ignored calls to leave the area but departed at 8:48 a.m. Thursday.

Japan’s Foreign Affairs Ministry lodged complaints with the Chinese Embassy in Tokyo and with the Chinese government in Beijing on Wednesday, a ministry spokesman said by phone Thursday. He called the situation “regrettable.”

The Senkakus, a string of five uninhabited islands and three rocks 105 miles east of Taiwan, are administered by Japan but claimed by both Taiwan and China.

A Chinese research ship last entered Japan’s exclusive economic zone in June 2022, the spokesman said.