Four Chinese patrol boats have temporarily entered Japan's territorial waters near the Senkaku Islands in the East China Sea.
The Japan Coast Guard says the ships entered the waters off Uotsuri Island shortly after 10 AM on Monday.
They stayed in the area for about an hour and 40 minutes.
Japan's government set up a taskforce at the prime minister's official residence in the morning to monitor the situation.
The entry into the waters off the Senkakus by Chinese patrol vessels is the fourth this year.
Japan controls the islands. The Japanese government maintains that the islands are an inherent part of Japan's territory. China and Taiwan claim them.