What caused five-alarm fire at Denver building? officials share insights

A fire at a Denver building has spread to the entire city block as firefighters were trying to contain the blaze on Friday, January 2, 2026.

Authorities said an under-construction building, Harker Heights, near Forest Street caught fire, prompting issuance of evacuation orders and stopping traffic from both sides.

The official cause of fire has not yet been determined; however, the Denver Fire Department has shared insights that fire rose to the level of “five-alarm fire”.

A five-alarm fire in the U.S. refers to an extremely large, severe blaze requiring the maximum response, calling in all available units and resources from multiple neighboring fire departments to control it and protect surrounding areas.

Denver Water increased the water pressure to help more than 100 firefighters trying to contain the blaze.

Denver Fire Department Division Chief of Operations Robert Murphy said that the absence of a dry wall to contain the fire in an under construction building makes the fire extremely difficult to contain.

He added: “It’s a complete city block and it is on fire and it’s unopposed because there’s no fire stops.”

Murphy said that the cause of fire is unknown, adding, “We don’t have any reason to believe that it was or was not started by somebody”.

The Fire Department has updated that a firefighter was injured while battling the flames and was taken to Denver Health for medical care.