A video of a police officer threatening to tie a homeless man to a pole during a blistering cold snap has provoked a storm of controversy in Montreal.

The video shows the officer initially reasoning with the man and urging him to find a place to warm up, before saying, "If I receive another 911 call about you, I will tie you to a pole for an hour."

The scene was posted to YouTube on Thursday as Montrealers experienced numbing cold. The temperature plunged to -27 C; with the wind chill, it felt like -41 C.

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The homeless man, clutching a cup in his hand, is standing outside a Montreal Métro station dressed only in a T-shift, cut-off jeans and sneakers, with a Santa cap draped over his shoulder. The officer tells the homeless man he had been the object of four complaints over aggressive behaviour while asking for change.

Mayor Denis Coderre weighed in on the video, calling the officer's behaviour "unacceptable." He said he spoke about the incident to police Chief Marc Parent.

The Montreal police also called the officer's words unacceptable, adding that he would be met by his commanding officer on Friday.

Matthew Pearce, Director General of Montreal's largest men's shelter, said police have made strides in dealing with the homeless in the city and called the incident a setback.

"The police can't afford to be saying these kinds of things. It's a bad technique to reduce tensions," said Mr. Pearce, head of the Old Brewery Mission. "In the deep cold, people can't survive out there."

His mission's 240 beds were full overnight and housed another 60 men on mattresses in the cafeteria. He said he was familiar with the man in the video, who is known to be homeless.

André Cantin, an Environment Canada meteorologist, said that human skin can freeze superficially within minutes with a wind chill of -40 C. Longer-term exposure can cause hypothermia.