Two Chinese government vessels entered Japan's territorial waters off the Senkaku Islands in the East China Sea on Friday.
Japan Coast Guard officials say they are warning the ships to leave the waters immediately.
The officials say the vessels intruded into Japan's waters off Minamikojima Island around 11:30 a.m. and approached a Japanese fishing boat. They say Japanese patrol ships are ensuring the safety of the boat.
The officials also say the two ships were among four Chinese government vessels earlier seen navigating in the contiguous zone, just outside Japan's territorial waters.
This is the 12th time this year that official Chinese vessels have entered Japan's territorial waters off the Senkaku Islands.
Japan controls the islands. China and Taiwan claim them. The Japanese government maintains the islands are an inherent part of Japan's territory, in terms of history and international law. It says there is no issue of sovereignty to be resolved over them.