Blinding snow contributed to a pileup on Highway 400 north of Toronto on Monday that involved as many as 75 vehicles, including a number of large trucks.
Ontario Provincial Police say two chain-reaction collisions occurred in opposite lanes near Highway 89 during whiteout conditions.
The accidents occurred at about 2 p.m. and closed both the north and southbound lanes. Mangled wreckage was littered across the highway.
Police officers and emergency personnel had to smash the windows of one passenger bus to rescue those inside.
"There were people trapped in the back of the bus, it was on fire ... the driver was still inside with possible broken legs," said Const. Dave Woodford, one of the first officers on scene.
"There was zero visibility. I could hardly see when I was coming down," he said of the conditions. "You couldn't see two feet in front of you."
A unknown number of people involved in the pileup were taken to local hospitals. The most serious injury involved the driver of a tanker truck who slammed into the back of a tractor-trailer. He was airlifted to hospital in critical condition.
Police said a jack-knifed tractor-trailer in the northbound lanes triggered many of the collisions.
Motorists were urged to avoid the area as the stretch of highway was expected to be closed in both directions well into the night.
Meanwhile, a serious accident in Halton Hills on Monday morning left one man dead and sent three others to hospital.
Drifting snow wreaked havoc on Toronto-area roads and highways all day.
"We're getting problems anywhere north of the 401, especially to the north and west," Sgt. Cam Woolley told CTV.ca on Monday afternoon.
"Literally hundreds of accidents have occurred since early this morning when we started getting the (strong) winds."
Driving was tricky because of fast-changing conditions. Moments of sunshine and clear visibility would suddenly change to high winds coupled with snow squalls, Woolley said.
The OPP closed a number of roads as a result of the severe weather, including all Dufferin County routes.
"This is only the beginning," Woolley said. "It's getting colder and windier and there's another storm headed in from the west."
Police have issued a warning about severe winter driving conditions throughout central and southern Ontario.
The OPP said wind gusts of up to 90 km/h out of the northwest were expected at times.
Police also said there was a possibility vehicles could be "pushed off" highways due to high winds.
Motorists were urged to drive with caution and avoid venturing out onto the highways whenever possible. Police also advised people to make sure they have enough fuel for their trip, reduce speed, and bring appropriate winter clothing.
For people with cellular telephones, police advised motorists to be aware of their location at all times. In an emergency, the OPP can be reached by calling *OPP (*677) from any cellular phone.
With a report from CTV 's Jim Junkin
