Japan's Coast Guard says four Chinese government vessels entered Japanese territorial waters off the Senkaku Islands in the East China Sea early Monday.
The Coast Guard says the ships entered Japan's waters near the islands of Uotsuri and Minamikojima.
They arrived at around 2:40 a.m. and stayed in the area for nearly 10 hours.
The vessels were reportedly approaching Japanese fishing boats. Coast Guard personnel told them to leave immediately.
This marks the 28th time this year Chinese government ships have entered Japanese 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.