A passenger plane carrying 181 people crash-landed on its belly on Sunday at an airport in South Korea, hitting a barrier and exploding into an orange fireball in the worst aviation disaster in the country in almost three decades.

Most of the people on board the plane, a Boeing 737-800 operated by Jeju Air, were killed, officials said.

The plane, Flight 7C2216, had taken off from Bangkok and was landing at Muan International Airport in South Korea’s southwest when it crashed around 9 a.m. local time. Officials said the plane had broken into so many pieces that only its tail was identifiable.

The plane was carrying 175 passengers and six crew members. As of Sunday evening, the official death toll had risen to 177, according to the National Fire Agency. Two crew members had been rescued from the aircraft’s tail section, and emergency workers continued searching the wreckage.

What caused the crash?

Officials were investigating why the landing gear appeared to have malfunctioned, and whether birds had struck the plane or if bad weather had been a factor, Ju Jong-wan, a director of aviation policy at the Ministry of Land, Infrastructure and Transport, said at a news briefing.

As the plane was landing, he said, the airport warned it about a potential bird strike. The plane issued a mayday alert shortly after, he said, then crash-landed.