Firefighters were called about 8:15 p.m. to the five-story KC Bolt, Nut & Screw Co. building at 12th and Hickory streets.
When they arrived, they found flames billowing from the roof, and the fire quickly spread to a nearby structure.
The buildings involved apparently were vacant.
Shortly after arriving, firefighters were forced to take a defensive posture around the building.
The cause of the fire was not immediately known. No one was believed to have been injured.
The 12th Street Viaduct was shut down from Hickory to Interstate 35 out of concern that the fire posed a risk to motorists.