TORONTO, Dec. 22 -- A massive weather system has left the largest Canadian city blanketed in a thick coat of ice, and nearly 300,000 people without power since early Sunday morning.

The bouts of heavy overnight freezing rain caused numerous complications on the road, disrupting travel and Toronto's transit service on one of the busiest travel weekends of the year.

Over 300 departing flights have been cancelled at Toronto Pearson International Airport since the morning.

With ice-coated tree branches toppling over across the city pulling down power lines, and more than 90 "large-scale outages" throughout the city, Toronto Hydro warned that many could be left without power until Christmas Day.

"The city is experiencing widespread outages. We cannot provide restoration time, please plan for a worst case - up to 72 hrs," Toronto Hydro, the largest municial electricity distribution company in Cananda, tweeted.

The freezing rain warning has been lifted in Toronto, but it seems the worst is yet to come.

Toronto Hydro is expecting high winds later Sunday, which could result in even more power outages. Winds are expected to gust as high as 50km/hr.

Calling the storm one of the worst in Toronto's history, Mayor Rob Ford said at a news conference Sunday afternoon that the city is not yet in a state of emergency, but that could change if the weather conditions continue to worsen over the next 24 hours.

Restoring power to the city's two hospitals is top priority, said Ford.

About 20 Toronto Community Housing buildings were also without power, according to the mayor, who urged city residents who have power to reach out to elderly friends, family members and neighbors in this time of need.