Swathes of the US are shivering through a vicious “life-threatening” cold snap that has forecasters urging anyone who braves the outdoors to “avoid taking deep breaths and to minimise talking”.

The extreme Arctic blasts from a polar vortex are forecast to hit much of America’s midwest from Wednesday to Friday (Australian time), bringing temperatures as low as -53 degrees.

The BBC reported that a state of emergency had been declared in the midwestern states of Wisconsin, Michigan and Illinois, as well as in the normally more clement southern states of Alabama and Mississippi.

With at least 55 million people across those states about to experience temperatures below freezing, Iowan officials warned of the “life-threatening weather” to come – and advised people to “avoid taking deep breaths, and to minimise talking” if they went outside.

“The intensity of this cold air, I would say, is once in a generation,” US National Weather Service meteorologist John Gagan said.

Coldest snap in more than 20 years across Iowa this week. LIFE-THREATENING cold is forecast. Please take this seriously! #iowaweather pic.twitter.com/87YzyXE6SP

— NWS Des Moines (@NWSDesMoines) January 27, 2019

The NWS warns that frostbite is possible within just 10 minutes of being outside in such extreme temperatures.

It says Chicago will be colder than Antarctica during the polar vortex. The Illinois city could experience a low of -33 degrees, with freezing winds making that feel closer to -46 degrees.

By Tuesday afternoon (local time), it was -16 degrees in Chicago, -12 in Detroit and -26 in Minneapolis.

As much as 60 centimetres of snow is forecast in Wisconsin, and 15 centimetres in Illinois.

The southern states of Alabama and Georgia are also expecting snow.

The brutal blast known as the polar vortex is a mass of freezing air that usually spins around the stratosphere over the North Pole. Its current has been disrupted and it is pushing south into the US.

“This could possibly be history-making,” said Ricky Castro, a National Weather Service meteorologist in Romeoville, Illinois.

Many cities in the Midwest had opened warming shelters. Regional governments closed hundreds of schools and airlines cancelled more than 1000 flights, including many destined for Atlanta, where the National Football League’s Super Bowl will take place on Sunday.

Amy Patterson, a vice president at the Atlanta Super Bowl Host Committee, said there was enough time for the freeze to pass to allow fans to fly to Atlanta in time for the game. The NWS has forecast a balmy 14 degrees for the city on Sunday.

The freezing weather has also caused some political controversy. US President Donald Trump took to Twitter to make his views clear:

In the beautiful Midwest, windchill temperatures are reaching minus 60 degrees, the coldest ever recorded. In coming days, expected to get even colder. People can’t last outside even for minutes. What the hell is going on with Global Waming? Please come back fast, we need you!

— Donald J. Trump (@realDonaldTrump) January 29, 2019

A few hours later, one of the US government’s meteorological agencies, the National Oceanic and Atmospheric Administration, responded in kind with what was widely interpreted as a rebuke:

Winter storms don't prove that global warming isn't happening. https://t.co/LDqfq4JH9n pic.twitter.com/ndmLD637Cb

— NOAA Climate.gov (@NOAAClimate) January 29, 2019

The freezing temperatures may also have killed a man in Minnesota. He was found dead outside his home on Sunday, according to a local media reports.

-with agencies