The Japan Coast Guard said Chinese patrol ships entered Japanese territorial waters Sunday off the Senkaku Islands in the East China Sea. 
Three Chinese ships were seen entering the vicinity of Uotsuri Island. The Coast Guard said they navigated Japanese waters for about 90 minutes, Japan's broadcaster (NHK World) reported. 
It was the first intrusion by Chinese patrol ships since January 4th. The Coast Guard has warned the vessels not to enter the waters again. 
A senior official with the Japanese Foreign Ministry lodged a protest by telephone with Chinese authorities in Tokyo. 
The ministry also filed a similar protest through the Japanese embassy in Beijing. 
Japan controls the islands. The government maintains they are an inherent part of Japan's territory. China and Taiwan claim them.

Source: QNA