Two people were killed in a massive explosion at a fireworks warehouse that rattled homes and sent up a cloud of smoke that could be seen for kilometres outside Montreal.

The subsequent inferno prompted a shutdown of the adjacent highway, causing a huge traffic jam, and an evacuation of surrounding homes and a campground.

Provincial police said two bodies were found in the wreckage.

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The initial explosion at B.E.M. Fireworks occurred just before 9 a.m. Thursday and completely destroyed the building, which was reduced to charred scraps.

A series of sparkly blasts followed.

A plume of thick, dark smoke emanated from the blast site, located near Valleyfield, Que., roughly 60 kilometres southwest of Montreal. The vibrations could be felt for kilometres and the smoke could also be seen from neighbouring municipalities.

"We got really, really, really scared," said Ginette Liboiron, who runs a convenience store across the highway overpass.

"I thought my store was falling to the ground. It shook like you can't imagine... We all went outside to see and saw the big, incredible smoke.

"Then the fireworks went off."

According to its website, B.E.M. has been designing and manufacturing pyrotechnics and fireworks for 25 years.

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One area resident said the explosion scared her cats. Another said his dog slammed into a wall.

The two panicked felines went scampering under the bed. Madeleine Boucher said she watched the explosion from her window 700 metres away.

"It was impressive," she said, joking that the incident would have prettier at night.

"Wasn't very pleasant, though... I wouldn't say I was scared for myself, no, but I'd have been scared if I lived closer."

Another man, whose dog slammed into the wall, was about to have breakfast with his wife.

Roland Desforges says his wife thought the explosion might have been a plane crash or an act of war. But he says he instantly suspected it might be the neighbouring fireworks plant.

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He says he went to the overpass to get a look.

He believes the initial explosion occurred in the middle of three buildings on the compound: in the production plant, which he says is centred between the fireworks store and its storage facility.

"In seconds there was nothing left," Mr. Desforges, 68, said of the plant.

The company occupies a sprawling property near Highway 20 that includes a store and warehouse. According to the Quebec business registry, the company employs between six and 10 people.

Ms. Liboiron said she has run the nearby store for 37 years and had never worried about being next to the fireworks factory.

That indifference went up in a cloud of smoke.

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"It was gigantic," she said of the smoke.

"It went high up in the air, then it became black, black, black."