Japan's Coast Guard says four Chinese government ships entered Japanese territorial waters off the Senkaku Islands in the East China Sea on Monday.
Coast Guard officials say the vessels intruded into the waters off Uotsuri and Taisho islands at around 4:30 p.m., and they are warning the ships to leave immediately.
This is the 16th time that Chinese government vessels have intruded into Japanese 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.