An explosion and fire at a refinery has sent smoke billowing over Great Falls.

Police officials blocked roads and told people living near the Calumet Montana Refinery to stay in their homes with their doors and windows closed on Thursday.

The threat was over that afternoon. Jeremy Jones of Great falls Fire Rescue says the fire was put out by an internal suppression system and fire brigade.

All employees have been accounted for, no injuries were reported and the air quality in the immediate area has been deemed safe.

Jones says he did not immediately know the cause of the fire, and said the investigation would be conducted by Calumet.

The refinery can process up to 25,000 barrels of crude oil a day into gasoline and other products for distribution in the Northwest and Canada.