Chicago Is About To Get Colder Than Everest And Antarctica

Americans have been told to 'avoid taking deep breaths and to minimise talking' as a once-in-a-generation deep freeze settles over the US.

More than 250 million people will endure below freezing temperatures on Wednesday, as a polar vortex sweeps across the States.

A state of emergency has been declared in Wisconsin, Michigan, Illinois, Alabama, and Mississippi, while the National Weather Service has warned that just 10 minutes outside could lead to frostbite.

Chicago will cop the brunt of it, the city is bracing for its coldest temperatures on record.

Pedestrians battle snow in Chicago on Monday (Terrence Antonio James/Chicago Tribune/TNS via Getty Images)

The mercury is expected to plummet to -32C on Wednesday, but paired with freezing winds, it will feel more like -46C.

That's colder than Alaska, Mount Everest and Antarctica.

“This storm poses a serious threat to the well-being of people around the state, and we will use every tool at our disposal to keep our residents safe,” state governor J.B. Pritzker said in a statement on Tuesday.

READ MORE: Does America's Extreme Cold Mean That Climate Change Is A Myth?

Shelters have been opened, thousands of schools and businesses are closed, planes are grounded, and for just the fourth time in history, the Brookfield Zoo has been shut down.

Crime is on the rise too, with Chicago police claiming people are being robbed at gunpoint for their warm coats.

The icy chill is all thanks to the polar vortex which is a mass of freezing air that usually spins around the North  Pole. Forecasters say it was pushed south by a blast of hot air from Morocco.

As expected, plenty of locals have piped up about the big freeze on Twitter.

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While U.S. President Donald Trump has chimed in, calling for global warming to "come back fast".