The Butte-Silver Bow Fire Department responded to a structure fire at the corner of Excelsior Avenue and Copper Street on Tuesday afternoon.
There were no injuries reported.
Firefighters found one half of a duplex burning, which was venting out the front windows of the structure.
They determined from police officers at the scene that no one was believed inside either unit.
Firefighters were able to knock down the main body of the fire within minutes, and then made entry into both units in order to conduct a search and check for fire extension.
Firefighters then spent a considerable amount of time conducting overhaul operations and assisting Fire Marshal Doherty in the cause/origin investigation.
The cause of the fire has not yet been determined.
The fire department received assistance from the BSB Law Enforcement Department, 911 Dispatch, A-1 Ambulance, Northwestern Energy Gas and Electric Divisions and the BSB Water Utility Division.