Japanese Coast Guard officials say a Chinese ship has apparently conducted a survey without consent in Japan's exclusive economic zone near the Senkaku Islands in the East China Sea.
The officials say a patrol boat spotted the ship dangling what looked like a cable into the sea about 89 kilometers off Uotsuri Island on Sunday morning.
The UN Convention on the Law of the Sea stipulates that prior consent is needed to conduct a survey in another country's exclusive economic zone.
The coast guard says China didn't seek consent.
The patrol boat asked the Chinese ship to stop the survey. But it didn't respond and left the EEZ about two hours later.
Chinese government vessels navigated just outside Japan's territorial waters for 64 days in a row until Friday.
That's the longest period since the Japanese government purchased some of the Senkaku Islands from a private Japanese owner in 2012.
Japan controls the Senkaku Islands. The Japanese government maintains the islands are an inherent part of Japan's territory. China and Taiwan claim them.