At least four people are dead and 15 others injured after a crash involving two tractor trailers and at least seven other vehicles in Laval on Monday afternoon.

The Sureté du Quebec the day after the crash that three of the people were in critical condition, while almost all of those injured had to be hospitalized.

Police are still trying to identify everyone involved in the crash, and autopsies will be necessary to identify some of the victims.

The cause of the pileup is still under investigation but it's believed that a car changed lanes in order to exit the highway, cutting off another vehicle.

On Tuesday Transportation Minister Francois Bonnardel said he would order changes to the highway markings so the painted line that prohibited drivers from changing lanes before the exit was extended.

Police said the heavy trucks were heading west on Highway 440 near Highway 15 when they crashed at 3:35 p.m.

On Monday one Laval firefighter said one of the truck drivers was not able to brake in time and hit another vehicle.

At least two passenger vehicles, including one appearing to be an SUV or a minivan, were crushed underneath the 18-wheelers in the collision.

One SUV rolled on its side and hit the fence between the highway and the service road, while a small black car spun out and hit the fence but remained upright.

One of the trucks then caught fire, and the flames spread to the other truck and another passenger vehicle.

The trucks were carrying food, but at least one of the vehicles was carrying propane tanks.

Emergency crews rushed to the scene and shut all lanes of Highway 440, east and west, until 5 a.m. on Tuesday.

Police could not say which vehicles were carrying the people who were killed.