Cities are all but shutting down across the US Midwest as the region shivers through a record-breaking and deadly cold snap known as a “polar vortex”.
At least six people are reported to have been killed across several states as a result of the arctic weather.
Temperatures have dropped as low as -45C (-49F) in Chicago and -54C in North Dakota.
Freezing weather will chill 250 million Americans, and 90 million will experience sub-zero temperatures.
Twenty million people in the continental US will experience temperatures of -28C or lower by the week’s end.
Snow is expected to fall throughout Wednesday, from the Great Lakes region into New England. As much as 24in (60cm) is forecast in the state of Wisconsin, and 6in in Illinois.
States of emergency have been declared in the Midwestern states of Wisconsin, Michigan and Illinois, and even in the Deep South states of Alabama and Mississippi.
“This could possibly be history-making,” said Ricky Castro, a National Weather Service meteorologist in Illinois.
Multiple deaths have been confirmed, including a man killed by a snow plough in Chicago; another found frozen to death in a Milwaukee garage; and a young couple who died after a traffic accident on snowy roads in northern Indiana.
How is it affecting daily life?
Hundreds of schools have been closed in the affected states.
At least 1,300 flights were cancelled early on Wednesday, mainly out of Chicago O’Hare and Chicago Midway international airports, said FlightAware.com.
The US Postal Service has also cancelled mail deliveries throughout the Midwest on Wednesday.
Even beer deliveries in Wisconsin have been hit by the cold, as brewers delay shipments over fears their beverages will freeze in the trucks.
The National Weather Service is warning that frostbite is possible within just 10 minutes of being outside in such extreme temperatures.
Residents of the city of Chicago in Illinois, long used to freezing winters, have been warned to expect an unusually deep and dangerous period of cold.
Chicago mayor Rahm Emanuel has urged people not to venture outdoors if possible. Dozens of “warming centres” for the estimated 80,000 rough sleepers there, including buses.
But at least one homeless Chicago man said he preferred to take his chances with the deadly weather, rather than go into a shelter.
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.”
Chicago landmarks including the Lincoln Park Zoo, Field Museum and Art Institute are closed.
Those braving the cold on Wednesday will also be hard pressed to find a warming cup of coffee – La Colombe has shut all five of its Chicago cafes, as have other local shops.
Delivery pizza – a traditional bad-weather food in the US – has also been affected. Chicago’s famous deep dish pizza chain Lou Malnatis and other regional restaurants closing early on Tuesday and Wednesday.
Chicago police say people are being robbed at gunpoint of their coats, especially those wearing Canada Goose jackets, which can cost as much as £900 ($1,100).
Weather officials in the state of Iowa have warned people to “avoid taking deep breaths, and to minimise talking” if they go outside.
Animal rights organisation Peta has warned people to bring animals indoors.
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 ahead of schedule, the farmers said, and newborn calves cannot survive such conditions.
Meanwhile, police in McLean, Illinois, some 150 miles (240km) from Chicago, had some fun with the freeze, announcing that Elsa, from Disney movie Frozen, had been arrested over the extreme cold.
What is causing this?
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.
How did President Trump inject controversy?
President Donald Trump, who has questioned whether humans are responsible for climate change, tweeted about the conditions.
“What the hell is going on with Global Waming [sic]?” he said. “Please come back fast, we need you!”