A section of Highway 401 west of Toronto has been reopened after treacherous driving conditions caused a multi-vehicle pileup on Saturday.

The 401 was temporarily closed between Port Hope and Cobourg after close to 30 vehicles -- including tractor-trailers, fire trucks and an ambulance -- were involved in a series of collisions due to treacherous driving conditions, the OPP said. As many as 10 people were sent to hospital.

Motorists who were involved in the collisions say visibility at the time was reduced to zero and blowing snow was covering the road.

"All of a sudden, we started seeing cars sliding in front and there was really nothing you could do," Craig Leis told CTV Toronto.

An airport shuttle bus carrying seven people was one of the vehicles involved in the multi-vehicle crash. It was sideswiped by a transport truck but everyone on board escaped without injuries.

A military unit headed to CFB Trenton from Toronto was able to help out stranded motorists, as emergency crews worked to clear the roads.

"The roads were horrible. White squalls everywhere and it wasn't long before we came by a lot of people that needed help," Corp. Glen Villa told CTV Toronto.

"We're assisting the firefighters here…some of us have medical training."

Officials had been asking residents to stay indoors as emergency crews work to clear the roads.

Saturday's multi-vehicle pileup unfolded less than 24 hours after another major crash also closed a section of the 401.