The incident occurred at about 5pm local time yesterday at the Boise Airport, the main airfield in the state’s capital city, Boise’s fire department division chief of operations Aaron Hummel said during a press conference.

“There was a large-scale collapse of the building, the framework of the building,” Hummel said. “It was a pretty global collapse that occurred and the main structural members came down. It was fairly catastrophic.”

Three people died at the scene. Nine other people were injured, including five who were in critical condition at local hospitals, the city said in a statement on its website.

Local authorities and US Occupational Safety and Health Administration officials were investigating the cause of the collapse, Hummel said.

A crane at the construction site also fell during the incident, Hummel said.

The Jackson Jet Center, which owns the building, said in a statement to local media that dozens of people were working on the construction site for its new 3,623sq m steel hangar.

Airport operations were not impacted by the incident, Boise’s fire department said in a post on X.