Americans are being told to limit their breathing and the amount of time they spend outside as temperatures in parts of the country are forecast to drop as low as -70C (-94F).
In Minnesota, where temperatures could drop as low as -70C (-94F) because of wind chills, the local National Weather Service office (NWS) tweeted an ominous warning.
“These are VERY DANGEROUS conditions and can lead to frostbite on exposed skin in as little as five minutes where wind chill values are below -50C (-58F). Best thing you can do is limit your time outside,” the office said.
The weather office in Des Moines, Iowa, where temperatures are expected to reach about -20C (-4F) on Wednesday, urged residents “to protect your lungs from severely cold air, avoid taking deep breaths; minimise talking.”
The worst of the weather is expected across the Midwest, and especially Chicago, which forecasters say could be colder than parts of Antarctica.
The Chicago River has frozen over, with large chunks of ice floating through the city section of the river.
More than 1,550 flights have been cancelled over Tuesday and Wednesday, and another 2,100 have been scrapped across the country on Wednesday, FlightAware.com said.
Businesses, government offices and schools have been closed on Wednesday in Chicago, America’s third largest city, along with major attractions like the Lincoln Park Zoo, Art Institute of Chicago and Field Museum.
The current freeze will not be limited to a few unlucky regions, however, as around 212 million, or 72% of Americans, will experience below-freezing temperatures over the next few days.
And more than 83 million Americans, or about 25% of the US population, will suffer subzero temperatures sometime between Wednesday and Monday.
Authorities in Illinois, Michigan and Wisconsin put emergency measures in place to handle the severe cold.
The frigid air heading across the US from west to east is driven by a brief visit by the polar vortex, a whirling mass of cold air circulating in the mid to upper levels of the atmosphere, present every winter.
It usually stays closer to the poles but sometimes breaks apart, sending chunks of Arctic air southward into the US during winter.
Conditions in parts of the country have become so extreme that postal workers won’t be out delivering anything in six entire states, and parts of four others.
There was time for some levity, however, as the McLean Police Department, in Illinois, “arrested” Elsa, the Ice Queen from the movie Frozen, for bringing the cold weather with her.