Three people were killed and nine were injured at the Boise, Idaho, airport when a hangar under construction collapsed Wednesday, CBS reports.

Five of the injured are in critical condition.

Authorities were called about 5:00 p.m. to the scene where the steel-framed shed suffered a “catastrophic” collapse, said Boise Fire Department Chief of Operations Aaron Hamel.

“It was a very chaotic scene, I don’t know what caused it,” Hamel added.

Boise airport operations were not affected, officials said.

Hamel said some of the victims were on a hoist or elevated platform at the time the hangar collapsed, requiring some specialized rescue efforts. He confirmed that a crane also collapsed in the incident.

Authorities are investigating what caused the collapse.