MONTREAL - A winter storm tearing its way across Ontario and Quebec has sent at least 29 people to hospital following a series of highway pileups in Montreal.

Blowing snow and black ice was blamed and Quebec provincial police called in extra help to deal with the multiple mash ups of cars and transport trucks.

The biggest sandwich took place on a highway east of Montreal which involved about 70 vehicles, including about 30 tractor-trailers and a school bus.

It stretched three kilometres long.

A provincial police spokesman on the scene says the accident sent three people to hospital with minor injuries, but no one on the school bus was hurt.

Another pileup north of Montreal produced an accordion of about 30 vehicles and sent four people to hospital -- one with serious injuries. Several tractor-trailers were also part of the wreckage.

Further down the same highway, 10 vehicles were involved in another pileup. And another accident, near Montreal, sandwiched 20 vehicles together.

One hospital says it has treated 29 people for accident related injuries.

Quebec provincial police spokesman Sgt. Denis Richard said it was a "big day" for accidents as the storm seemed to catch motorists off guard.

"I've seen pileups before, but that many pileups all over the place? It's been a while," he said.

"It's out of the ordinary."