Firefighters later determined that the fire was burning in mostly wooden construction, Bennyhoff said.
By 8 p.m., flames were shooting through the roof of three-quarters of the building and the fire was visible through windows and where walls had fallen. Firefighters used a defensive, or exterior, attack through much of the night because of the fire's intensity and its effects on the structure, Bennyhoff said.
The Great Falls Police Department responded to the brewery less than two hours before Great Falls Fire/Rescue were called, Sgt. Dean Bennett said. Police were called because of reports of juveniles in the building, but there was no indication that they were responsible for the fire.
"There were some kids in the area prior to the fire being set," Bennett said. "It's certainly a possibility."
"There's been kids in there all the time," said Marty Nelson, who lives kitty-corner from the old brewery.
An October 2002 fire inside the vacant brewery was believed to be arson.
Fire officials said no one was injured in Sunday's fire.
McCamley said that because of the nature and size of the fire, crews expected to be on scene into the morning hours.