Cities are all but shutting down across the US Midwest as the region shivers through a deadly cold snap known as a polar vortex.
At least six people have been killed in several states as a result of the arctic weather.
Temperatures fell to -30C (-22F) in Chicago - colder than parts of Antarctica - and -37C in North Dakota.
Freezing weather will chill 250 million Americans, and 90 million will experience -17C (0F) or below.
Snow is expected to fall throughout today, from the Great Lakes region into New England. As much as 24 inches (60cm) is forecast in the state of Wisconsin, and 6 inches in Illinois.
States of emergency have been declared in Midwestern Wisconsin, Michigan and Illinois, and even in the normally warmer Deep South states of Alabama and Mississippi.
"This could possibly be history-making," said Ricky Castro, a National Weather Service (NWS) meteorologist in Illinois.
The NWS is warning frostbite is possible within just 10 minutes of being outside in such extreme temperatures.
Grand Forks, North Dakota, has seen the lowest wind chill so far at -54C.
Twenty million people in the continental US will experience temperatures of -28C or lower by the week's end.
A man was killed by a snow plough in Chicago and another man froze to death in a Milwaukee garage.
An 82-year-old man died from hypothermia outside his home in Pekin, Illinois, NBC News reported.
A young couple died after a collision on snowy roads in northern Indiana.
The US Postal Service has called a halt to mail deliveries in parts of 10 states in the Great Plains and Midwest.
Hundreds of schools, as well as colleges and universities, have been closed in the affected states.
Beer deliveries in Wisconsin have been hit, too, as brewers delay shipments for fear their beverages will freeze in the trucks.
Weather officials in the state of Iowa have warned people to "avoid taking deep breaths, and to minimise talking" if they go outside.
Farmers across the Midwest have been taking measures to protect their livestock, including building igloos for chickens.
In North Dakota, cattle ranchers Joey Myers and Scott Bailey told Reuters news agency they planned on staying up with their animals during the cold snap to prevent fatalities.
Frigid weather could cause pregnant cows to deliver prematurely, the farmers said, and newborn calves cannot survive such conditions.
Animal rights organisation Peta has warned people to bring animals indoors.
But police in the Illinois county of McLean had some fun, announcing that Elsa from the Disney movie Frozen had been arrested.
Residents of America's third largest city are no strangers to perishing cold, but they have been warned to expect an unusually dangerous freeze.
Chicago has seen more than 1500 flights cancelled from its two main airports, and rail operator Amtrak has scrapped train services from its hub there.
With the icy breeze whipping off Lake Michigan, the Windy City will feel more like -45C.
Chicago mayor Rahm Emanuel urged people not to go outside if possible.
Dozens of "warming centres" have been opened for the estimated 80,000 rough sleepers there.
But at least one homeless Chicago man said he preferred to take his chances outdoors.
Tony Neeley told the New York Times: "A lot of us don't go to the shelters because of bedbugs. We don't go because people steal from you.
"We don't go because you can't even really sleep in the shelter."
The Illinois city's landmarks, including the Lincoln Park Zoo, Field Museum and Art Institute, are all shut.
A number of coffee shops and other local businesses have closed and even some of its famous deep-dish pizza parlours are shutting early.
Chicago police say people are being robbed at gunpoint of their coats, especially those wearing Canada Goose jackets.
The bitterly cold conditions are the result of a spinning pool of cold air known as the polar vortex.
It normally circles the stratosphere over the North Pole, but its current has been disrupted and it is now moving south into the US.
Forecasters are attributing this to a sudden warming above the North Pole, caused by a blast of hot air from Morocco last month.
This weather system split the polar vortex and caused it to drift south, Judah Cohen, a winter storm expert for Atmospheric Environmental Research, told AP news agency.
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
President Donald Trump, who has questioned whether humans are responsible for climate change, tweeted on Tuesday about the conditions.
"What the hell is going on with Global Waming [sic]?" he said. "Please come back fast, we need you!"
But one of the US government's own meteorological agencies, the National Oceanic and Atmospheric Administration, posted an apparent rebuttal.