US anticipates brutal weather from a dangerous Arctic blast

Millions of people hunkered down Sunday in America in anticipation of brutal weather from a dangerous Arctic blast that could send US temperatures plummeting to their coldest in 20 years.

The northeast of the country and parts of Canada have been in the grip of crippling heavy snow and deadly sub-zero conditions since the turn of the year and the deep freeze is now ripping through the US Midwest and threatening usually balmy areas further south.

The wind chill from the rare "polar vortex" could make it feel as cold as -60 Fahrenheit (-51 Celsius) in places, weather forecasters say, prompting authorities in several towns and cities to issue warnings that people should stay indoors and even stock up on food.

In such extreme cold, exposed skin would suffer frostbite in as little as five minutes, experts have cautioned.

In Colorado, parts of which were under a "wind chill advisory" warning of "very cold air and strong winds," a small plane burst into flames on landing near Aspen on Sunday, killing one person on board, officials said.

Two other people were injured in the accident at the snow-blanketed airport in the exclusive ski resort town, the Pitkin County Sheriff's Office confirmed, without specifying a cause. The small jet had taken off from Tucson, Arizona.

In New York, which declared a state of emergency when storm Hercules swept in on Thursday, John F. Kennedy Airport ceased operations for more than two hours because of freezing rain and snow after a Delta Airlines jet from Toronto slid into a snowbank.

None of the 35 people on board were hurt, ABC News said, but at least a dozen people have died in the cold conditions and travel has been badly disrupted, with thousands of flights canceled or delayed, ensuring a miserable end to the holiday season for some.

The National Weather Service described the weather as "life-threatening."

"The coldest temperatures in almost two decades will spread into the northern and central US today behind an Arctic cold front," it said.

"Combined with gusty winds, these temperatures will result in life-threatening wind-chill values as low as 60 degrees (Fahrenheit) below zero. Also, heavy snow will develop from the eastern Plains to the Great Lakes today, with up to a foot of accumulation possible."

The Midwestern states of Minnesota, where Governor Mark Dayton has already announced schools will be closed Monday "to protect all our children from the dangerously cold temperatures," and North Dakota were expected to experience the worst weather.

Chicago, Detroit and St Louis all saw more snowfall overnight, caking cars, pavements and any exposed ground in piles of dense snow, while Sunday's National Football League playoff showdown between the Green Bay Packers and the San Francisco 49ers at the open-air Lambeau Field in Wisconsin looked set to be one of the coldest NFL games in history.

The Packers say they will help fans battle the big freeze by handing out free coffee, hot chocolate and hand warmers, while supporters would also be allowed to bring blankets and sleeping bags.

Added to the mix was freezing rain forecast to hit the south and east, affecting New England, New York and Washington, with the extreme weather expected to continue into the early part of the week in many places.

Several weather warnings were in place across more than half of the United States, including for blizzards, gales and flooding.

The Weather Channel said the country should be prepared for an imminent "blast of brutally cold air" that would buffet some states until Tuesday.

Among the deaths blamed on the weather was a worker killed on Friday when he was crushed by a 100-foot (30-meter) 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.