Authorities urged Americans to stay indoors and stock up on food after a fierce winter storm killed 11 people and forecasters said the Arctic blast could bring record low temperatures.
There was no sign of respite Saturday from the brutal chill that has struck since the start of 2014 in parts of the northeastern United States and Canada, prompting New York and New Jersey to declare a state of emergency.
Following heavy snowfall Thursday, one of the coldest Arctic outbreaks in the past two decades is set to plunge America's Midwest close to record cold conditions.
Chicago could on Monday see some of its most bracing weather ever, with temperatures hovering around minus 10 degrees Fahrenheit (minus 23 Celsius), weather analysts said.
Gusty winds could bring what forecasters at the National Weather Service called "very dangerous levels" of wind chill.
"Incredibly, it may feel as cold as -50 to -60 (Fahrenheit) on Sunday night over sections of the north-central states with the frigid air remaining in place into early next week," it said.
In such conditions, exposed skin would suffer frostbite in as little as five minutes, forecasters cautioned.
Authorities have urged people in the worst-hit areas to spend the first weekend of the new year at home for their own safety and to allow rescue and clean-up teams to get to work as quickly as possible.
"Chicagoans are a hearty bunch," said Matt Smith, spokesman for the Chicago Department of Family and Support Services.
"But when temperatures get as cold as they are predicted, you want to start thinking out things in advance," the Chicago Tribune quoted him as saying, adding that the department had advised people stay indoors and ensure they have medical supplies and food.
In Minnesota, Governor Mark Dayton has already announced schools will be closed Monday "to protect all our children from the dangerously cold temperatures."
The storm has been the first big test for New York City's new Mayor Bill de Blasio, who only took up his job Wednesday.
"If you want safe, clear streets, stay home," he said Friday.
In an unrelated incident, New Yorkers' attention was at least temporarily distracted from the weather when a private plane was forced to land on a highway in the city's Bronx borough due to engine trouble, injuring the pilot and two passengers.
Thousands of domestic and international flights have been canceled or delayed in several US cities including at New York's John F. Kennedy Airport and in Chicago, Boston and Philadelphia, while thousands of miles of roads were also snarled.
Added to the mix was a flood alert for much of the Atlantic coastline of Massachusetts.
Coldest NFL game ever?
On Friday, a worker was killed when he was crushed by a 100-foot (30-metre) pile of salt being prepared to treat roads in the Philadelphia area, media reports said.
A 71-year-old woman suffering from Alzheimer's disease froze to death after walking out into the cold and getting lost in northern New York state, according to authorities.
At least nine other deaths were blamed on the storm, nicknamed Hercules.
Eastern Canada has also been badly hit, and residents in many parts of Newfoundland lost power, local media reported.
Temperatures there had plunged to five degrees Fahrenheit, but the wind chill made it feel as cold as minus 31.
The bracing weather was also set to impact Sunday's crucial National Football League playoff between the Green Bay Packers and the San Francisco 49ers.
Some media outlets speculated that the eagerly anticipated clash at the open-air Lambeau Field in Green Bay, Wisconsin, might be the coldest NFL game in history as freezing temperatures and blustery winds threatened a windchill factor as low as minus 35 degrees Fahrenheit.
The Packers say they will help fans battle the big freeze at the open-air stadium by handing out free coffee and hot chocolate.
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