The explosion happened just before 9 a.m. at a fireworks factory southwest of Montreal, QMI Agency reported.
Firework continued to go off after the explosion, fueling the fire. Cars parked outside the building were destroyed, the news report said.
When firefighters arrived on the scene they were not immediately able to approach the building, CNN reported.
Nearby residences and other businesses were evacuated as a precaution, authorities said.
The cause of the explosion has yet to be determined. The identities of the two people who died in the explosion were not available.