Four patrol ships of the Chinese maritime police on Wednesday entered the area off the disputed Senkaku (Diaoyu) Islands in the East China Sea, which Japan considers its territorial waters, Kyodo news agency reported.

According to it, Japan's Maritime Safety Administration issued a warning to Chinese ships to leave the area. Meanwhile, Chinese ships have been near the Senkaku Islands for the past 20 days.

The dispute over the Senkaku Islands escalated after Tokyo announced in September 2012 that they were buying them from private owners who are Japanese citizens. After that, mass protest demonstrations took place in the PRC, accompanied by the destruction of Japanese restaurants and enterprises. Since then, Chinese ships have been constantly cruising near the disputed archipelago and making demonstrative visits to its coastal zone.