A Chinese military airplane entered South Korea's air defense identification zone without notice on Monday, less than a month after the last such reported intrusion, Seoul's military authorities said.

The Air Force deployed some 10 fighter jets to track the aircraft and send a warning message to the aircraft, the Joint Chiefs of Staff said.

The Chinese plane first entered the KADIZ from northwest of South Korea's southern island of Jeju at around 11 a.m. and flew out of the zone toward Ieo Island, a submerged rock south of Jeju.

Before finally leaving the zone at 3:53 p.m., the plane entered the KADIZ two more times from the southeastern city of Pohang and from Ieodo, the JCS explained.

Air defense identification zones are not territorial airspace.

They are areas each country zones off to prevent foreign planes' infiltration. (Yonhap)