Vo Huy Cuong, deputy head of Civil Aviation Authority of Vietnam, said they were cooperating with South Korean peers to find out why a Boeing 737 plane of South Korean airline T’way Air had to make an emergency landing in Ho Chi Minh City in the first hours of Thursday.

The front of the plane was damaged as it landed at Tan Son Nhat International Airport, but how the damage occurred remains a mystery.

"Normally if the plane hits a bird, there should be blood traces but there was nothing in this case," he said.

Airport officials said that the captain of the plane, which was on its way from Seoul to HCMC, informed the airport of some technical problem after he heard a big noise in the front of the aircraft.

The aircraft was about to land and was staying at a height of over 2,000 feet. Once the noise was heard, the captain asked for permission to make an emergency landing, which was granted.

As the plane with 166 passengers touched down safely, technical staff at the airport identified a dent in the front as well as several cracks.

The airplane has been parked at the airport for further checks.