Authorities responded to the collapse at around 5pm on Wednesday at a privately owned steel-framed hanger under construction, Boise Fire Department Operations Chief Aaron Hummel said in a news briefing.
As of Wednesday evening, everyone who had been at the site had been accounted for, Mr Hummel added.
Three people died at the scene, and five of those who were injured are in critical condition and are receiving care at local hospitals, the city said in a statement on Wednesday.
Fire crews worked to stabilise the scene and were able to rescue multiple victims, the statement added, with Mr Hummell also telling local news that some of the rescue efforts were challenging, but a technical rescue team made entry and were able to rescue those people.
“I don’t know what caused it, but I can tell you it was a pretty global collapse,” Mr Hummel said. “It was fairly catastrophic.”
A crane also fell during the incident, Mr Hummell added.
Emergency and trauma teams were also at the scene with first responders to treat the victims, Leticia Ramirez, a spokesperson for Saint Alphonsus Regional Medical Center in Boise, said, according to Associated Press.
The response efforts included eight fire engines, three ladder trucks, two safety officers, two battalion chiefs, one division chief, a heavy rescue unit, and a dozen ambulances, the city statement said.
They added that the names of the victims who died will be released by the Ada County Coroner’s Office after their families have been notificatied.
While the structure was on Boise Airport’s property, it is not an airport project and construction was being carried out by a private party, which was in the early stages and only had the framework up, Boise Airport director Rebecca Hupp said at the news briefing.
Jackson Jet Center, a private airplane charter company, said in a statement that the collapse occurred just west of their existing centre.
It happened “at our new 39,000-square-foot steel hangar under construction, where dozens of dedicated people were working on site” the company’s statement said in part, according to Idaho News 6.
“We do not know exactly what caused the hangar collapse,” the statement added. “Our focus now is on supporting our team and partners during this difficult time.”
Idaho senator, Mike Crapo, said on X that he was aware of the collapse in Boise and added that his “prayers are with those injured and emergency responders.”
Operations at Boise Airport have not been impacted, and the site is secure with no threat to the public.
Authorities are investigating what caused the collapse of the hangar.