Billings Fire Battalion Chief Ed Regele said no one was in the structure at the time the fire started around 3:18 p.m.
Firefighters had the blaze knocked down 30 minutes later.
Regele said structure appeared to him to be a paintless car dent repair shop. A sign on the front of the structure read "Auto Hail Repair."
The fire was mostly contained to the west end of the building, Regele said. Some smoke permeated into the building's east end, causing damage.
Initially, firefighters had to force entry into the structure because all the doors were locked. For this task they used handheld power saws.
To ventilate smoke from the building, firefighters sawed a hole in a garage door that had become inoperable during the fire.
Regele said preliminary investigation work has been done to determine the fire's cause, but investigators will return to the scene in the daylight hours for further inspection.
The Billings Fire Department will remain on scene through the night to monitor the structure.
Five engines from the Billings Fire Department and one truck company responded to fight the fire.
At around 3:15 p.m. Sunday, the Billings Fire Department, the Billings Police Department and AMR all responded to a structure fire in the area of South 30th St. and 1st Ave. South.
The structure appears to be an Auto Hail Repair shop, with smoke pouring out of the building.