A Chinese maritime survey ship was spotted early Sunday near the Senkakus, a group of Japan-controlled islets claimed by China, and ignored a warning by a patrol boat against conducting survey activities, the Japan Coast Guard said.
The coast guard said the patrol boat Motobu spotted the 3,235-ton Dongfangfong No. 2 maritime survey ship at around 5:50 a.m. in Japan's exclusive economic waters in the East China Sea, about 24 km southwest of Uotsuri, the main island of the Senkakus.
The islets are known as Diaoyu in China.
The Chinese ship conducted survey activities until Sunday night without giving advance notice, the coast guard said. This was the first unauthorized survey by the Chinese near the Senkakus in roughly two years, officials said.
In the evening, Foreign Ministry officials lodged a complaint with the Chinese Embassy in Tokyo for the lack of advance notice. The embassy replied it would "check the facts" pertaining to the incident, according to Japanese officials.
The Chinese ship sailed in a northwesterly direction while apparently performing research operations such as taking seawater samples.