SEOUL -- A total of 122 people, including passengers and crew members, were evacuated Friday as smoke filled the cabin of a passenger jet in South Korea's airport, according to Yonhap news agency.

The unidentified smoke flowed into the cabin of a Jin Air aircraft, which was scheduled to fly from the international airport in the country's southern resort island of Jeju to the southeastern port city of Pohang, at around 12:25 pm local time (0325 GMT).

While boarding was underway, all 122 passengers and crew members were evacuated as an internal alarm went off in the cockpit following the detection of smoke.

According to the inspection of the aircraft, the smoke was believed to have been caused by a defect in the auxiliary power unit (APU) located in the tail section of the plane, resulting in overheating.

The APU serves as a backup engine that supplies electrical power and air conditioning when the main engines are shut down.