Toronto declared its first extreme cold weather alert of the season Thursday as cold air swept in following a winter storm.

Officials said they decided to declare the alert, which offers extra services to homeless people, because many people living on the streets aren't used to the cold weather yet.

An alert usually comes into effect when Environment Canada predicts a temperature of -15C or lower. Toronto's temperature was expected to drop to -10C overnight.

Earlier Thursday, the first major winter storm of the season caused numerous traffic problems and school bus cancellations across southern Ontario.

In Toronto the city's transportation department was out early to attack the snow and freezing rain.

"At five this morning we sent the salt trucks out on expressways and main roads," said Peter Nohammer, director of transportation services.

"We've got about 200 trucks in our arsenal [and that's] probably what we've got out on the streets right now, or close to it."

Sanders and plows kept busy

Nohammer said the city's trucks and plows would stay out through the day.

"We'll be continuing with our salting operation and as the snow starts to accumulate we'll determine whether we go out with another round … and if we need to clear any snow or slush, we'll make that call through the day as well."

North of Toronto numerous vehicles slid into ditches because of the slick driving conditions, said police.

By 8 a.m. the OPP was reporting more than 100 accidents - by noon that number had tripled.

"It's snowing quite heavily up here," said Const. Dave Woodford.

"Most of our collisions have been single motor vehicle collisions, vehicles into the ditch that slid off the road … no injuries so far," he reported during an interview on CBC Radio's Metro Morning.

"It's moving slow right now on the 400 and 427 … people have to slow down, they can't travel that normal speed they're used to, they have to make sure they keep a safe distance from the vehicle in front."

Dozens of flights delayed

The storm is also affecting air traffic in and out of Toronto. Dozens of flights were delayed or cancelled.

The poor conditions prompted several school boards to cancel their school bus runs.
 
All school buses in Simcoe County and York Region were cancelled and in Durham Region north of Highway 7. The Dufferin Peel Catholic district school board, the Waterloo district Catholic board and the Peel district board also cancelled buses.
  
About 800 school buses are also idled in the Trenton, Belleville and Kingston areas, giving some 20,000 students a day off school. Some buses have also been cancelled in Brighton and Campbellford.
  
Snow, freezing rain and ice pellets are expected to blanket a region from Kitchener-London region east to the Kingston area. Environment Canada said many areas can expect 10 to 15 centimetres of snow.

Nohammer said Ontarians should get used to it. "It's a fact of life of living in Canada and that we deal with snow and we have to adjust."

With files from Canadian Press