More than 38,000 hydro customers in areas west and north of Toronto were without power early Thursday as freezing rain began coating wires and tree branches with ice.
PowerStream, which services communities north of the city, was reporting some 28,000 residents and businesses without power in the Vaughan. Woodbridge and Kleinburg areas.
Ontario Hydro was working to restore power to more than 10,000 customers, primarily in the Fergus, Listowel, Cambridge and Kincardine areas, with restoration expected to be completed by around mid-morning
Environment Canada warned that between five and 20 millimetres of ice accumulations were possible before the freezing rain changed to rain on Thursday afternoon as temperatures slowly inch toward zero.
The federal agency also cautioned people to take extra care navigating slippery and potentially hazardous surfaces such as highways, roads, walkways and parking lots.
Once the freezing rain ends, some areas were expected to receive anywhere from 10 to 25 millimetres of rain.
The icy weather will also mean a day off for thousands of students across southern Ontario.
Classes and buses have been cancelled at the Dufferin-Peel Catholic District School Board, the Peel District School Board and at Halton Catholic schools. Both the Toronto District School Board and the Oxford County board have cancelled buses, but schools remain open.
In eastern Ontario, Environment Canada said significant freezing rain was expected to begin Thursday afternoon.