Chicago (AFP) – A blast of bone-chilling cold snarled air travel, closed schools and prompted calls Tuesday for people to stay inside in the United States and Canada, as temperatures plunged to lows not seen in two decades.

Superlatives of cold-talk abounded, even in midwestern states used to chest-high snow and bitter cold, as the National Weather Service said the deep freeze was making its way east.

Air travel was a nightmare, stranding many travelers trying to head home from year’s end holidays.

More than 4,300 U.S. flights were canceled Monday — nearly half of those in Chicago — and more than 6,500 were delayed, according to FlightAware, a flight-monitoring site.

Toronto’s Pearson Airport 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.

Flights were scheduled to resume at 9:00 am local time, but police were reinforced at the airport amid rising tension among stranded travelers.

Airline JetBlue said it was reducing operations at four airports in the bustling northeast corridor — JFK, La Guardia, Newark and Boston — until 10:00 am Tuesday.

More than a dozen deaths were blamed on the frigid weather.

A shift in a weather pattern known as the “polar vortex” triggered a drastic drop in temperatures to lows not seen in two decades.

It coincided with wind chill warnings in much of the eastern United States.

Comertown, Montana recorded the lowest wind chill value so far at minus 63 Fahrenheit (minus 53 Celsius) while North Dakota, South Dakota and Minnesota were not much warmer.

That was significantly colder than the South Pole, which recorded a wind chill reading of minus 29 degrees Fahrenheit.

In Minneapolis, Minnesota, where people scoff when cities like Washington D.C. panic and shut down with even a moderate snowfall, the newspaper The Star Tribune gave a graphic description of what happens when, for instance, the overnight temperature Monday hit minus 23 Fahrenheit.

“The wind chill and cold are freezing exposed flesh in five minutes,” it said.

The paper said life has “slowed to a crawl across the state.”

“It’s a blistering cold spell destined for Minnesota winter weather lore,” it added.

Even the typically temperate Deep South was feeling the chill with a hard freeze warning threatening crops and livestock.

Early Tuesday in Washington D.C., the temperature was a relatively mild 12 degrees Fahrenheit (minus 11 degrees Celsius) early Tuesday, but blustery winds blew leaves and trash swirling in the air.

Deaths blamed on the frigid weather included a 71-year-old woman suffering from Alzheimer’s disease who froze to death after getting lost in New York state.

The body of a 90-year-old woman was found face down in the snow next to her car in Ohio on Monday morning, the Toledo Blade reported.

At least a dozen other people were reportedly killed in crashes on icy roads, including four people whose sport utility vehicle slid off a rural Minnesota highway and fell into the Mississippi River.

Four Chicago men aged 48 to 63 died of apparent heart attacks while shoveling snow over the weekend, the Chicago Tribune reported.

The cold snap came after two massive winter storms snarled travel, grounded thousands of flights and dumped as much as two feet of snow in the first few days of the year.

Chicago was among scores of towns and cities which told parents to keep their children at home rather than risk sending them out into winds so bitter that skin could freeze in a matter of minutes.

The governor of Minnesota canceled school across the entire state on Monday.

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

“We are facing a dangerous combination of low temperatures, black ice and snow drifts,” Quinn said, as he urged people to stay off the roads.

Quinn praised the “heroic” efforts of National Guard troops who cleared a 375-vehicle backup and a forestry officer who rescued seven stranded people and two of their pets using a snowmobile.

In Milwaukee, Wisconsin, officials warned residents to stay indoors and urged schools to shut down as temperatures dropped to minus 12 Fahrenheit, (minus 24 degrees Celsius) with the wind chill making it feel like minus 37 Fahrenheit (minus 38 Celsius.)

“Police are reaching out to homeless citizens in order to help them find the nearest shelter,” city spokeswoman Sarah DeRoo told AFP.

Indianapolis mayor Greg Ballard barred everyone except emergency workers from driving at the height of the storm Sunday and urged residents to stay indoors unless absolutely necessary on Monday.

“This extreme cold poses a serious health and safety risk,” he warned.

But with thousands of people without power after electrical lines were felled, home was not always the best option.

Those who couldn’t stay with family or friends were urged to seek out community centers which were opened as temporary shelters.

The extreme cold disrupted flights and classes in Canada as well. The Atlantic island province of Newfoundland had more than 30,000 people without power.

Nationwide, officials warned of “treacherous” travel conditions, but meteorologists said a warming trend would begin mid-week.