The aircraft carrier Liaoning and five other Chinese warships have sailed north in the high seas between the Okinawa’s main island and Miyako Island, the Defense Ministry said.

The incident occurred on Tuesday morning. The same six vessels were found entering the Pacific after sailing south from the East China Sea on April 11, according to the ministry.

It was the first time for the Liaoning to travel back and forth in the area. None of the Chinese warships crossed into Japanese territorial waters or the contiguous zone around the territorial waters, the ministry said.

Maritime Self-Defense Force destroyers and patrol aircraft spotted the six Chinese ships sailing at a point some 80 kilometers southeast of Miyakojima around 9 a.m. Tuesday.

After 10 a.m., the six vessels entered the East China Sea after traveling north between the Okinawa main island and Miyako Island, the ministry said.