NHK said the Liaoning sailed between the islands of Yonaguni and Iriomote in the southern Okinawa region, temporarily entering the "contiguous" zone adjacent to Japan's territorial sea.

The defence ministry was unable to immediately confirm the news reports.

Contiguous waters are a 12-nautical-mile band that extends beyond territorial waters.

The move comes as Japan strongly protested early this month after a Chinese naval ship entered its territorial waters.

And last month, Japan scrambled fighter jets after what it called the first confirmed incursion by a Chinese military aircraft into its airspace.