THE polar vortex is here – and tens of millions of people in the United States are bracing for a deep arctic chill, which authorities say could be life-threatening.

Sub-zero temperatures already blanketing parts of Canada are already sweeping across the U.S. Midwest and towards the East Coast.

The big chill in the Midwest came on the heels of a major storm that dumped up to 30 cm of snow on the region over the weekend – and reportedly claimed at least two lives so far.

“We need everyone to do your part and make sure you and your families are prepared,” said Illinois Governor JB Pritzker.

Companies told their workers to stay home. Schools were closed. Hundreds of flights were canceled.

Temperatures in almost a dozen states stretching more than 1,930 km from the Dakotas to Ohio were forecast to be the coldest in a generation, if not on record.

“One of the coldest arctic air mass intrusions in recent memory is surging south into the Upper Midwest before spreading across much of the eastern two-thirds of the country,” the National Weather Service said.

“Expect frigid temperatures, bitterly cold and life-threatening wind chills, likely leading to widespread record lows and low maximum temperatures from the Upper Midwest to the Great Lakes and Ohio Valley.”

The culprit? A swirl of arctic air that broke away from the polar vortex that usually encircles the North Pole.

The National Weather Service forecast temperatures between -23 to -40 degrees Celsius by yesterday across the Midwest, with wind chills making it seem even colder.

Chicago, America’s third largest city, was expected to be colder than parts of Antarctica.

Authorities in Illinois, Michigan and Wisconsin put emergency measures in place to handle the frigid weather.

Americans were asked to stay home if possible yesterday, when temperatures were expected to be at their coldest. Scores of schools, businesses and government agencies announced closures in multiple states. “People exposed to extreme cold are susceptible to frostbite in a matter of minutes,” warned the NWS.

In the northeastern and southern U.S., snow was falling. A cold emergency was declared in the U.S. capital Washington, with additional services put on for the homeless.   (SD-Agencies)