( CNN ) -- Two people died Thursday when a fireworks plant exploded near Montreal , federal police in Quebec said . `` You could see the fireworks going off , '' said Stacey Hylen , who was bicycling with her husband and 5-year-old daughter to a nearby school to watch her 10-year-old participate in a mini triathlon . `` The kids thought it was fireworks for the start of their triathlon , '' Hylen , 41 , told CNN in a telephone interview . The plant is located a mile north of the school in the town of Coteau-du-Lac , nearly an hour 's drive southwest of Montreal . As the explosions continued , it became clear that was not the case . `` It was like a bomb , '' she said . `` It was so loud . Like , at first you were thinking it was dynamite . It just kept going on and on . And then , when you saw the mushroom cloud it was like , woah ! It just freaked me out . It shook . I had friends tell me it shook their house , and they live miles away . '' Soon after , thick black smoke emerged from the roof of one of the factory 's two buildings , both corrugated-metal structures about 20 feet tall . The children were sent into the school gymnasium , she said . `` The cloud was really black and scary looking . You did n't want to breathe it . '' Fireworks shot from one building to the other , about half a football field away , and both structures were soon in flames , she said . Across the parking lot , a store that sells fireworks and souvenirs was unscathed , she said . Soon , police and fire vehicles arrived , but firefighters were initially unable to approach the buildings , which continued to be rocked by explosions . Highway 20 , which connects Montreal with Toronto , was shut in both directions for hours . Residents and businesses within a kilometer of the BEM plant were evacuated as a precaution , Quebec Provincial Police Sgt . Joyce Kemp said . An investigation was under way to determine the cause of the fire , she said . The triathlon was canceled . CNN 's Justin Lear contributed to this report .
` ` You could hear the fireworks go off , '' said mother who is from a nearby school . Everyone within a mile of the plant is watching . The plant is nearly an hour 's drive south of Montreal .