Japan has accused China of conducting unnotified maritime scientific research within its exclusive economic zone around its southernmost island in the Pacific Ocean, Tokyo said Tuesday.

The alleged activity took place on Monday near the remote atoll of Okinotori in the Philippine Sea roughly halfway between Taiwan and Guam. China has said it does not constitute an island.

Japan's coastguard on Monday spotted a Chinese maritime survey vessel "extending what appeared to be a wire into the waters in Japan's exclusive economic zone (EEZ) 270 kilometers east of Okinotori island," government spokesman Yoshimasa Hayashi told reporters.