A person with a walker crosses Canfield Avenue in Detroit, Michigan

Frostbite warnings were issued for parts of the American Midwest on Wednesday as temperatures colder than Antarctica grounded flights, forced schools and businesses to close and disrupted life for tens of millions.

Mail deliveries were suspended and residents encouraged to stay home in nearly a dozen US states where temperatures overnight plunged into the negative double digits, the worst freeze to grip the region in a generation with all-time records still under threat.

US media have attributed at least five deaths since the weekend to the freezing conditions and a major snowstorm that preceded the blast of Arctic air currently gripping the region.

Chicago residents awoke to blocks of ice floating on the downtown river of America's third-largest city and flames from gas burners heating regional commuter rail lines to keep them functioning.

The morning temperature in the Windy City was -22 degrees Fahrenheit (-30 Celsius), which felt like -50 degrees (-46 Celsius) with wind chill. It was colder than Alaska's state capital and even colder than parts of Antarctica.

More than 1,500 flights were canceled at Chicago's two major airports while rail operator Amtrak scrapped train services from its hub in the city.

The US Postal Service—known for its commitment to bringing the mail whatever the weather—suspended deliveries in parts of Indiana, Michigan, Illinois, Ohio, Iowa, the Dakotas and Nebraska.

Mail deliveries were suspended, schools and business closed, and residents encouraged to stay home in nearly a dozen states where temperatures overnight sank into the negative double digits, the worst cold to grip the region in a generation

The cause of the sub-zero chill was a swirl of arctic air that broke away from the polar vortex that usually encircles the North Pole.

"There's cold, and then there's COLD!" the National Weather Service (NWS) said. "Extreme and dangerous COLD!"

"A record arctic air mass will remain over the central and eastern US over the next several days," the NWS said.

"Wind chill values of 30 to 60 degrees below zero will be common across the northern Plains, Great Lakes, and upper Midwest," it said. "If you can't stay cozy inside, be sure to cover any exposed skin."

A bicyclist braves the cold in downtown Minneapolis, Minnesota

Homeless at risk

Residents in Grand Forks, North Dakota, faced a bone-chilling -35 degrees Fahrenheit, with wind chill temperatures as low as -63, and it was -27 degrees in Minneapolis, Minnesota.

Authorities warned that the extreme temperatures were life-threatening, as Illinois, Michigan, and Wisconsin implemented emergency measures.

"We need everyone to do your part and make sure you and your families are prepared," said Illinois Governor J.B. Pritzker. "There is a real risk of hypothermia and frostbite."

Warming centers were opened for vulnerable residents such as the elderly and shelter capacities increased for the homeless, including the approximately 16,000 people estimated to live on the streets of Chicago.

Jen Brackman and Aaron Brackman don heavy jackets and goggles while on a walk on the Stone Arch Bridge in Minneapolis, Minnesota

"We're adding extra beds at shelters," Chicago Mayor Rahm Emanuel told a news conference Tuesday. "No one in need of a safe or warm place to stay will be turned away."

In Chicago and Minneapolis, buses were used as roving warming shelters for the homeless.

Chicago's regional electric train service was canceled due to wire problems caused by freezing temperatures, as gas burners heated rail switches to keep trains moving on a reduced schedule.

North America faces arctic chill

Authorities and health experts warned that frostbite and hypothermia can could set in in minutes in the extreme cold.

Remnants of a weekend snowstorm continued to plague portions of the northeast—with strong winds and blowing snow threatening whiteout conditions and reducing visibility.

Heavy snow was forecast in the northern stretches of Maine and snow squalls were predicted for other parts of the east coast of the country.