Northwestern Energy's main office in uptown Butte caught fire early this morning around 6:30am.
Investigators told NBC Montana the fire started in the basement of the building.
" Every Wednesday morning at 6:30 we have an emergency generator that exercises and this morning for some reason the electrical part of that caught on fire, there were actually flames down there and a lot of smoke" Said John Stenson, the manager of facility services for Northwest Energy.
Nobody was injured in the fire but the building did sustain smoke damage.
Around 200 employees work in the building and they're now working from home or other locations.
There is no word yet on when the building will reopen.