Twenty-five firefighters from the Boulder Fire Department have been fighting a fire at a duplex at 408 and 410 Arapahoe Avenue. Multiple 911 calls came in to the communication center around 3:12 a.m.

When firefighters arrived, the duplex at 410 Arapahoe was fully involved.

Five adults were inside. Two have been transported to Boulder Community Hospital to be evaluated for smoke inhalation injuries. Another is being flown to University Hospital to be treated for severe burns.

At this time, the fire is out. Firefighters are pulling down ceilings and knocking down walls to make sure there are no hot spots inside and that no smaller fires are continuing to burn in unseen areas.

Investigators are on-scene. The cause of the fire is undetermined at this point, and it’s too early to estimate damages to the building.