(File photo)

Japanese Coast Guard said they saw a Chinese research vessel pulling something like ropes under the sea on Thursday morning, about 310 km northeast of Okinotori island.

Japanese Chief Cabinet Secretary Yoshihide Suga said the vessel anchored in the area until the next morning. Japan via diplomatic channels has requested China immediately end its activities.

Chinese vessels often travel around Okinotori, a coral island which Japan selected as a mark for its EEZ of 200 nautical miles.