The Quebec Transport Ministry says it will review the configuration of a highway exit in Laval, north of Montreal, where four people were killed in a crash Monday afternoon that involved at least eight vehicles, including two trucks.

The accident happened around 3:30 p.m. ET on Highway 440 westbound when a small car collided with an 18-wheeler near the exit to Highway 15.

The two vehicles then hit a second truck, starting a pileup involving another six vehicles and a major fire, with plumes of black smoke that reached high above the city. One car became stuck underneath one of the trucks.

Provincial police investigators are working with the coroner's officer to identify the victims of the crash.

Three people remained in critical condition Tuesday and nine first responders were treated for smoke inhalation.

Investigators collected statements from witnesses, but are asking anyone who saw the collision or has video of it to contact them — which can be done anonymously at 1-800-659-4262.

"Some of the vehicles are in such a damaged state that it's not easy to find the [serial] numbers that identify them," said Sûreté du Québec Sgt. Daniel Thibodeau on Tuesday morning.

Quebec Transport Minister François Bonnardel, centre, speaks to reporters a day after the fatal collision with Finance Minister Eric Girard, left, and Laval Mayor Marc Demers, right. (Radio-Canada)

Another fatal collision happened at the same exit in 2016.

Transport Minister François Bonnardel said his ministry will look at the provincial police investigators' report when it's ready to see what improvements can be made.

In the meantime, he said, the painted line separating the service lane from the highway will be extended a few hundred metres to dissuade motorists from moving into the service lane "at the last minute."

Terry Blanchard, who works by the scene of the collision, heard two loud booms, and when he looked out the window, it was clear it was a deadly accident.

"All we saw were flames. One truck looked like it hit the back of another truck," he said. "I've never seen anything like that before."

He said the smoke went so high that it blocked the sun.

A small car collided with a semi-trailer truck on the highway in Laval, about 27 kilometres north of Montreal. The two vehicles then hit a second truck, starting a pileup. (Submitted by Peter Christakos)

Driving in the area regularly, he said, the configuration of the highway where it connects with Highway 15 could have contributed to the accident.

But he also said he often sees reckless drivers on the road.

"You've got people cutting in. There's just a lot going on at once."

Mario Lévesque said he sees accidents at that stretch of highway all the time, and drivers often go from travelling at high speeds to being bumper to bumper.

"There are regularly three or four accidents per week," he said, though not as severe as Monday's collision.

Watch footage from the collision below.

Fiery wreckage is seen from a pileup involving two trucks and seven cars on westbound Highway 440 in Laval. Four people died in the collision. 1:07

Highway reopened

One of the trucks had about 10 propane tanks inside, but the Laval fire department said Tuesday that the tanks were empty. The fire department had the blaze under control around 5 p.m. that day.

Crash scene specialists spent the night collecting physical evidence and the busy highway was reopened to traffic around 5 a.m. Tuesday.

Thibodeau said it's too early to determine the cause of the crash.

"Nothing is off the table at this point. We're still gathering as much information as we can and the public's help would be much appreciated."