Two people were killed and more than two dozen others were injured Wednesday in a pileup involving more than 100 vehicles on a highway south of Montreal that the authorities said may have been caused by snow, wind and a sudden whiteout.

The accident took place around 12:30 p.m. in the southbound lanes of Highway 15 in La Prairie, Quebec, where the road runs alongside the St. Lawrence River. The pileup was more than half a mile long, according to the police.

Videos from the scene on Wednesday afternoon showed cars, trucks and buses that had been crushed or totaled, some of them half-covered in snow, as emergency responders worked to find and rescue people who were still stuck on the highway.

Sgt. Marie-Michèle Moore, a spokeswoman for the Quebec provincial police, said in an interview on Thursday that the pileup involved about 140 cars, about half of which were damaged. In addition to the two people who were killed, at least 29 people were injured and taken to hospitals, one of whom was in critical condition, she said. That person’s life was not considered to be in danger, she added.