The eastern half of the United States shivered yesterday as a dangerously cold whirlpool of dense air known as a "polar vortex" threatened to break decades-old records and freeze exposed skin within minutes.
The bitter weather comes after a heavy snowstorm hit much of the region last week. Officials closed schools in Chicago and other Midwest cities and warned residents to stay indoors.
Thousands of flights out of major airports such as Chicago O'Hare International and New York's John F. Kennedy were delayed or cancelled on Sunday due to weather-related problems. At O'Hare, one of the country's busiest airports, more than 1,300 flights were cancelled.
"It's just a dangerous cold," said National Weather Service meteorologist Butch Dye.
The forecast is extreme: minus 35 Celsius in North Dakota, and minus 26 in Minneapolis, Indianapolis and Chicago. Wind chills - what it feels like when high winds are factored into the temperature - could drop to minus 50.
"It hasn't been this cold for almost two decades in many parts of the country. Frostbite and hypothermia can set in within minutes," said Douglas Brunette, an emergency room doctor in Minneapolis
"I have seen frostbite occur through clothing. It's not enough just to be covered. You need clothes made for the elements. You need to repel the wind."
Indianapolis mayor Greg Ballard upgraded the city's travel emergency level to "red", making it illegal for anyone to drive except for emergencies or seeking shelter. The last time the city issued such a warning was 1978.
Watch: Sub-zero arctic blast strikes northeastern United States
Many cities came to a virtual standstill. Schools, government offices and courts in several states closed. In New York city, the temperature was expected to drop sharply from 11 degrees to minus 12 overnight as the arctic air moved in.
Southern states were bracing for possible record cold temperatures, too. With two freezing nights ahead, Louisiana citrus farmers could lose any fruit they cannot pick in time.
For several Midwestern states, the bitter cold was adding to problems caused by a weekend snowstorm. The National Weather Service said the snowfall at Chicago's O'Hare totalled more than 28 centimeters as of 6pm on Sunday.
Missouri transportation officials said it was too cold for rock salt to be very effective, and several Illinois roadways were closed because of drifting snow.
Many cities came to a virtual standstill. In St Louis, where more than 25 centimetres of snow fell, the Gateway Arch, St Louis Art Museum and the local zoo were part of the seemingly endless list of things closed. Even Hidden Valley Ski Resort, the region's only ski area, shut down.
School was called off yesterday for the entire state of Minnesota, as well as cities and districts in Wisconsin, Illinois and Indiana and Iowa. Chicago school officials reversed an earlier decision to keep schools open at the 11th hour.
Temperatures are expected to dip close to freezing today in parts of Florida, where citrus crops will be under threat.
Additional reporting by Agence France-Presse