A hangar under construction on the grounds of the airport in Boise, Idaho, collapsed today, killing three people and injuring another nine, officials said.

Five of those injured in the collapse at the Boise Airport are in critical condition, the city said in a statement released today.

Authorities responded about 5pm yesterday local time (1pm NZ time) to the incident at the privately owned steel-framed hangar after the “catastrophic” collapse, Boise Fire Department operations chief Aaron Hummel said during an earlier news briefing. Everyone who had been at the site had been accounted for at that time, he said.

The city statement said the three people killed died at the scene. It said responding fire crews worked to stabilise the scene and rescued multiple victims.

“It was a very chaotic scene,” Hummel said, describing the incident as a “large-scale collapse” of the framework of the building. “I don’t know what caused it, but I can tell you it was a pretty global collapse,” he said.

Boise Airport operations were not impacted, officials said.

Terra Furman was driving on Interstate 84 about 5.30pm when she spotted at least 20 police cars, ambulances and firetrucks about 400m from the entry to the airport. They were around what she described as a crane folded in half and a building collapsed into the shape of an M.

Authorities respond to the scene of hangar collapse at the Boise Airport. Photo / AP

“The walls were still up at a point and the middle collapsed in on either side,” she said.

Hummel said some of the victims were on a hoist or other elevated platform when the structure fell, and that required some specialised rescue efforts. He confirmed that a crane also collapsed in the incident.

Leticia Ramirez, a spokeswoman for Saint Alphonsus Regional Medical Center in Boise, said emergency and trauma teams were working with first responders to treat patients who arrived from the scene.

Authorities are investigating what caused the collapse. It happened next to Jackson Jet Center, which offers private airplane charters and maintenance.

Boise city permitting records show the contractor Big D Builders had obtained permits to build a 3623sq m jet hangar for Jackson Jet Centre.

The US$6.2 million ($10.14m) project was to include the construction of a concrete foundation and a metal building. Messages left by phone and email seeking comment from Big D Builders were not immediately returned.

Jessica Flynn, chief executive of Jackson Jet Center, said in a statement that the facility staff’s “hearts go out to everyone affected by this horrific event”.

Flynn said the collapse happened just west of the existing Jackson Jet Center at a site where the company’s new hangar was under construction. She said dozens of people were working on the site.

“We do not know exactly what caused the hangar collapse,” Flynn said. “Our focus now is on supporting our team and partners during this difficult time.”

James Quintana was driving to the airport when he saw emergency vehicles rushing past him. He said he immediately thought it was a plane crash. He then saw the collapsed hangar and paramedics tending to victims.

“I’m retired law enforcement and when there is that much commotion, that many emergency personnel and vehicles, there is something huge that has taken place,” he said. “It was a scary sight.”

Cody McGowan was working about 91m from the building when he said he heard something that sounded like a loud dog whine. When he looked up, he saw a hangar as tall as 3½ to four storeys collapsing in on itself and part of the crane on top.

“When I walked up there, you’re just kind of like, ‘Wow’,” he said. “It’s shocking to see a building falling in on itself.”