Japan has protested to China after six Chinese coast guard vessels approached disputed East China Sea islands accompanying a fleet of hundreds of Chinese fishing boats.

Japan's Foreign Ministry said in a statement it summoned Chinese Embassy officials after Japan's coast guard spotted the vessels Saturday along with a fleet of 230 Chinese fishing boats swarming around the Japanese-controlled Senkaku Islands. China also claims the islands.

Japan is demanding the ships leave the area.

China's coast guard vessels routinely sail around the islands, but the ministry said that the fleet's size showed "an escalation of the situation that could heighten tensions in the waters."

Japan also protested Friday after two Chinese coast guard ships entered the Japanese-claimed waters around Senkaku.

There has been no immediate comment from Beijing.