Toronto Mayor John Tory and city officials are blaming extreme weather as the cause behind the city's fourth massive power outage in just three years.

After an extensive blackout in Toronto on Tuesday that hit more than 250,000 residents, Mr. Tory and Toronto Hydro CEO Anthony Haines spoke about the outage Wednesday, which has left about 4,500 customers remaining without power. They cited Tuesday evening's freezing rain as the reason behind the blackout, and the weather in general for the frequent outages in recent years.

"I would point out first and foremost that the reason we're having more frequent outages is because we're having more frequent extreme weather," Mr. Tory said to reporters. "That's been a pattern that's been happening for a number of years, not just in Toronto, but in places all around the world."

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Mr. Haines said that Tuesday night's outage was caused in large part by the mixture of road salt with ice on the city's hydro poles, acting as a conductor of electricity. That, in turn, led to more than 50 of the city's hydro poles catching fire throughout the evening and night.

He said he hoped that by Thursday morning at the latest power would be restored to the remaining residents still affected by the outage. But with another deep freeze expected for Wednesday night, he warned of another "difficult night ahead."

The outage was just the latest in a string of similar incidents in recent years. A summer flood and December ice storm both caused massive blackouts in 2013. And Hurricane Sandy in 2012 also led to power outages for tens of thousands of Toronto residents.

"It's absolutely the new normal … it's unprecedented, these extreme cold weather events" said Councillor Jaye Robinson, who chairs the city's public works committee.

Ms. Robinson said that council has been working to set aside money for contingency funds in such events, and also ensuring capital investments are being made to update and upgrade infrastructure.

"David Suzuki warned us about this years ago, and now it's coming to fruition," she said.