Japan lodged a protest Monday with Beijing over the Chinese ships that are repeatedly intruding into Japan's territorial waters near the Senkaku Islands in the East China Sea, Chief Cabinet Secretary Yoshihide Suga said.

"It is extremely disappointing and regrettable that the intrusions by Chinese official vessels have occurred frequently," Suga told reporters in Tokyo.

His comments came after four China coast guard ships entered Japanese territorial waters near the Senkakus on Monday.

The intrusion, which occurred around 9:30 a.m., was the first since Oct. 1 and the 68th since Japan effectively nationalized the chain in September 2012.

Suga said Japan lodged a serious protest through diplomatic channels and call on China to immediately withdraw the vessels.

After a Japanese patrol ship told the Chinese vessels to leave Japanese waters, one of the four responded in Chinese and Japanese that the uninhabited islets have been "China's inherent territory since ancient times," according to the 11th Regional Coast Guard Headquarters in Naha, Okinawa Prefecture.

Earlier, the Chinese ships were seen sailing in the contiguous zone outside Japan's waters from shortly after midnight Sunday to around 2:30 a.m. Monday.