Firefighters responded to a fire at a warehouse in north Denver on Monday afternoon. The Denver Fire Department said the fire was burning at 5001 Colorado Boulevard. Firefighters initially said the building was a marijuana warehouse, but later said it was not. Crews completed an initial search and transitioned into defensive attack due to the amount of fire, meaning they were fighting the fire from the outside in. A plume of black smoke was visible in the area. The fire department said around 5:30 p.m. that the majority of the fire had been put out. Due to the size of the building and the extent of the fire, crews remained on scene to extinguish hot spots.