A snowstorm Wednesday crippled the GTA, stranding motorists, causing a number of multi-vehicle crashes and claiming the lives of at least two people.

A 46-year-old man was killed after his truck collided with a Durham Transit bus in Whitby amid whiteout conditions Wednesday morning.

Durham Regional Police say that the man was travelling eastbound on Nichol Avenue when he lost control of the vehicle, crossed a median and collided with the bus at around 9:30 a.m.

The bus was forced off the road and into a ravine. Two out of the three passengers on board the bus were taken to hospital but have since been treated and released.

In Markham, a 61-year-old woman was rushed to hospital without vital signs after she crashed her car at 14th Avenue and Ninth Line.

Police were called to dozens of additional crashes as the troublesome combination of falling temperatures, snow and strong winds made roads slippery and caused near-blinding conditions.

Ontario Provincial Police announced a number of closures across the Highway 400 series. Pile-ups involving between 20 and 50 vehicles were reported across the Greater Toronto Area.

Provincial police received thousands of calls for service and at one point, operators were fielding about a call a minute.

Even the TTC felt the effects of the weather as spokesperson Brad Ross announced several bus route cancellations. Other bus routes are being diverted because of slippery road conditions.

GO Transit is also reporting delays of up to 60 minutes on most bus routes.

Motorists are being warned to take it slow during the afternoon commute.

"There is no real need to rush getting home," Const. Hugh Smith told CP24 Wednesday morning. "We want everyone to get home safely, so just take your time and know that the environment has changed and that your tires aren't going to work as well."

While it causes problems on the ground, the storm is also affecting air travel in cities on both sides of the border with a number of airlines issuing travel advisories.

By 7 p.m., more than 220 departing and 180 arriving flights had been cancelled at Pearson International Airport.

The GTA saw snowfall amounts of between 15 to 18 centimetres, with 10 cm reported at Pearson and 19 cm in Mississauga, according to a report issued by Environment Canada shortly after 8 p.m.

The snowfall is being matched with the return of frigid air and strong wind gusts. The temperature will plunge to -17 C overnight, with a wind chill near -30.

As a result, the City of Toronto issued an extreme cold weather alert to increase services for the homeless. A wind chill warning was also issued for the city and much of southern Ontario Wednesday afternoon.

Winter storm warnings issued

The heaviest snow is expected in communities along Lake Erie and northeastern Lake Ontario.

Environment Canada issued winter storm warnings from Windsor to Niagara Region in the southwestern portion of the province and Napanee to Cornwall in the east.

In those regions, total snowfall amounts of 15 to 25 cm are expected by Wednesday night and near-blizzard conditions are possible.

Blowing snow warnings were issued for the Hamilton and Sarnia areas, where more than 15 cm of snow is possible until the low-pressure system moves on.

The snow is expected to taper off during the early evening hours.

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