Canadian police say whiteout conditions that came about suddenly most likely triggered a massive, deadly pileup involving about 200 vehicles south of Montreal.

Key points: Police were seeking to identify two people found dead inside their vehicle

Police were seeking to identify two people found dead inside their vehicle The pileup of vehicles stretched for about a kilometre after heavy winds off the St Lawrence River created sudden blizzard-like conditions

The pileup of vehicles stretched for about a kilometre after heavy winds off the St Lawrence River created sudden blizzard-like conditions Canada's Transport Minister said the highway is not known for any particular safety issues

Two people were killed and about a dozen people were sent to hospital with minor to serious injuries after the midday crash in La Prairie, Quebec.

Quebec's public safety agency said the two people who died were found trapped in their vehicle, and were in the process of being identified.

Clearing the highway took several hours as authorities tried to stabilise a diesel spill on the site.

The crash occurred around 12:30pm (local time) on a stretch of Highway 15 that runs along the St Lawrence River. The pileup of vehicles stretched for about a kilometre.

More than 200 cars were involved in the massive pileup. ( The Canadian Press/AP: Paul Chiasson )

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.

"People were driving, there were strong winds … and, suddenly, you couldn't see anything,'' Mr Bonnardel said. "And then, well, the pileup started.''

Two snow removal operations took place in the area in the hour before the incident, he noted.

Mr Bonnardel said the highway is not known for particular safety issues and 65,000 vehicles use the southbound part of it on a daily basis.

The Transport Minister said he will await the results of an investigation before deciding if any particular measures need to be taken.

A school bus was involved in the crash, but none of the high school students were injured. ( The Canadian Press/AP: Paul Chiasson )

Police spokesman Sergeant 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.

About 150 people were taken by bus to a nearby community centre for treatment and to be picked up.

Sergeant 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.

AP