Four people are dead and 12 others injured after a small car got stuck underneath a semi-trailer, causing a major accident Monday afternoon on Highway 440 in Laval, Que., about 27 kilometres north of Montreal.

Four people are dead and 12 others injured after a small car got stuck underneath a semi-trailer, causing a major accident Monday afternoon on Highway 440 in Laval, Que., about 27 kilometres north of Montreal.

After the car and semi-trailer struck each other they collided with another truck, said Christian Grand'Maison of the Laval fire department. That started a chain reaction that eventually involved another six vehicles. One of these also got stuck underneath a semi-trailer, Grand'Maison said.

Provincial police had initially said only three vehicles were involved with the crash.

The collision ignited a large fire, and smoke could be seen from several kilometres away.

Three people were pronounced dead at the scene. A fourth body was found in the wreckage Monday evening.

Twelve others were taken to hospital, including some first responders. Three of those are in critical condition, police said.

First responders discovered about 10 small canisters of propane inside one of the trucks, along with household items.

Grand'Maison said the propane may have triggered a minor explosion. The other truck was transporting vegetables.

The fire broke out around 3:30 p.m. ET Monday, near Industriel Boulevard. Firefighters had the blaze under control by 5 p.m.

Highway 440 is an east-west route that runs between Highways 13 and 25. The highway reopened to traffic at around 5 a.m. Tuesday.

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