Four Chinese government ships navigated in Japan's territorial waters off the Senkaku Islands in the East China Sea on Tuesday morning.

Japan Coast Guard officials say the vessels entered waters near Kubashima Island one after another from around 9:45 a.m. and stayed there until past 11:40 a.m.

As of 11:50 a.m., the ships were said to be in the contiguous zone just outside Japan's territorial waters, about 24 to 31 kilometers north of Kubashima.

The coast guard has been continuing to warn off the Chinese boats and monitor the area.

This is the sixth time this year that Chinese government vessels have been spotted entering Japan's territorial waters off the Senkaku Islands.

Japan controls the islands. The Japanese government maintains the islands are an inherent part of Japan's territory. China and Taiwan claim them.