Transport Minister Francois Bonnardel told reporters in Quebec City the pileup took place in an area where heavy winds come off the river, creating sudden blizzard-like conditions. Two snow removal operations took place in the area in the hour before the incident, but strong winds blew snow back into the roadway from the nearby river.
“People were driving, there were strong winds ... and, suddenly, you couldn't see anything,'' Bonnardel told reporters. "And then, well, the pileup started."
A group of American tourists from New York who were at the front of the pileup told Canada's CTV News they pulled onto the highway and faced a "pure white snow like a whiteout" before pulling to the shoulder as the crashes began.
Spencer Jacob told CTV an ambulance responding to an initial crash was hit by an ambulance at "full speed" before a chain-reaction crash was underway.
"Another car came down and just flew into the back of the ambulance. That blocked up two lanes and then another 18-wheeler came and just slammed into that car," Jacob said. "That's when we were like 'this is bad,' and we need to get out of the car. Our doors were pressed against the snow so we had to get out of the windows and run up onto the snowbank and we were just watching."
The group said they tried to wave to other cars to slow down but "they couldn't see" due to the conditions. The group continued to watch cars slam into each other as the crashes mounted to cover a half-mile-long stretch of highway.
"It was straight out of a movie," Jack Sandberg told CTV News.
Police spokesman Sgt. Stephane Tremblay said about 50 vehicles were able to drive away from the collision, but 75 others would need to be towed. Numerous vehicles were mangled, including several large trucks. The two people killed in the crash were in the same vehicle, according to officials
"We know that these people were involved in a collision with a tank truck, which made the rescue operation more difficult for first responders," Tremblay said Wednesday.
A total of 60 were injured in the crash, including 20 in serious condition, CBC News reported.
About 150 people were taken by bus to a nearby community center for treatment and to be picked up.
Tremblay said police crash experts will study what caused the pileup.
A school bus was also involved in the pileup, but none of the high school students on board were injured, said Andree Laforest, the province's acting public security minister.
The Associated Press contributed to this report.