More than a million people were left without power in eastern Canada Wednesday night after a storm damaged power lines, AFP noted.

In the province of Quebec, the Ministry of the Environment warns of freezing rain, authorities warn that “accumulation of ice can break tree branches.”

More than 945,000 Hydro-Quebec customers were without power as of 1 a.m. GMT Thursday, out of a total of 4.5 million. “The damage is mainly caused by falling branches or trees bending under the weight of the ice,” the power supplier explained on its website.

Almost half of those (440,000) were in Montreal, where city crews worked to clear roads damaged by fallen trees and downed power lines.

The city’s police received “a large number of calls about black ice,” while Quebec City Mayor Valérie Plante called for vigilance.

In the neighboring province of Ontario, more than 112,000 customers were without power after the winter storm “caused trees and branches to fall onto power lines,” according to Hydro One.

In the Canadian capital, Ottawa, the alarm was raised in the evening.