A DEADLY CHILL still has much of the United States and Canada in its wintry grip, as the record-breaking cold snap brings temperatures lower than on the surface of Mars.

Authorities have opened shelters for the homeless and anyone else who needed a warm place, and have reported at least 21 cold-related deaths across the country since Sunday, including seven in Illinois, and six in Indiana.

At least five people died after collapsing while shoveling snow, while several victims were identified as homeless people who either refused shelter or didn’t make it to a warm haven soon enough to save themselves from the bitter temperatures.

In Missouri on Monday, a 1-year-old boy was killed when the car he was riding in struck a snow plough, and a 20-year-old woman was killed in a separate crash after her car slid on ice and into the path of a tractor-trailer.

Polar bear

It was so cold in Chicago that the polar bear at the Lincoln Park zoo was brought inside to warm up, and she had not built up the winter fat stores of her wild cousins.

In Kentucky, an escaped inmate begged to be let back into prison so he could warm up after spending the night shivering in an abandoned house.

All of Canada and all the US states bar tropical Hawaii recorded temperatures below freezing on Tuesday, even usually sunny and warm Florida and California.

But the most dangerous cold, that can cause frostbite in a minute and death in a matter of hours, hit the Midwest as the ‘polar vortex’ brought frigid air from the Arctic.

A homeless man who wanted to be identified as John, tries to stay warm on a steam grate in Washington. (AP Photo/ Evan Vucci)

Schools, businesses and government offices were closed. Water mains and household pipes froze. Airplanes were grounded, trains were halted and roads and sidewalks became ice rinks.

The town of Embarrass, Minnesota, recorded the lowest temperature in the United States yesterday at a frigid -37 Celsius.

Factoring into wind chill, temperatures dipped as low as -52 Celsius in Montana and was in the -40 to -50 Celsius range in parts of Illinois, Indiana, Iowa, Maryland, Michigan, Minnesota, Nebraska, North Dakota, Ohio, Pennsylvania, South Dakota, Virginia, West Virginia and Wisconsin.

That’s cold enough to toss a cup of boiling water into the air and watch it turn into snow before it hits the ground.

Colder than Mars

The Mars Rover has been sending back daily temperature readings from its tour of the Red Planet ranging from -25 to -31 degrees Celsius.

“To be fair, though, Mars is still way colder,” the Smithsonian Institute wrote in a blog post.

The Curiosity rover is driving around in a crater at, roughly, the equivalent latitude of Venezuela.

But then again, Mars is 78 million miles further away from the Sun.

For a more Earthly comparison, the Amundsen-Scott South Pole Station recorded a temperature of -23 Celsius and a wind chill factor of -35 Celsius on Tuesday.

Brutal chill

The brutal chill came as people in the Great Lakes region were still digging out from two massive snow storms which dumped more than two feet of snow.

More than 500 people spent Monday night stuck on a train that was stranded by snowdrifts on the line between Detroit and Chicago, while nearly 2,500 flights were cancelled in the United States on Tuesday and 3,400 were delayed.

That brought the total of flights cancelled since the latest snowstorm hit on Thursday to more than 18,000.

Toronto’s Pearson Airport temporarily halted ground operations early Tuesday because of “equipment freezing” and out of concern for the safety of airport personnel, it said on its Twitter account.

Police reinforcements were called in to the airport to deal with rising tension among stranded travellers.

The governor of Illinois declared a state of emergency Monday and called up the National Guard to help rescue stranded motorists as high winds whipped up blinding snow.

Guardsmen were also deployed in Indiana and New York, a Pentagon spokesman told AFP.

Even hardy Canadians were complaining of the cold amid widespread power outages.

Meteorologists predict the cold snap will ease of Wednesday.