The fire began Sunday afternoon, but was only brought under control late in the evening.
The flames were so intense that St-Donat firefighters called in crews from five other surrounding municipalities to help them battle the fire.
St-Donat is near Mont-Tremblant and is approximately 125 kilometres north of Montreal.
According to Sgt. Benoit Richard of the Sûreté du Québec, the ashes had to be completely extinguished before investigators could examine the site.
He said the fire could have started behind a commercial area near 450 Principale Street while some of the businesses were still open.
Investigators will resume their search for answers Monday morning.