A massive blizzard bringing more than two feet of snow and punishing winds is advancing up the US East Coast.
More than 50 million people across more than a dozen states have been warned to stay at home as it moves north.
The nation's capital, Washington, could lie under a record 76 centimetres of snow by the time the storm passes on Sunday.
Eight people have been killed, six states have declared states of emergency and thousands of flights have been cancelled.
The weather system affects a huge swathe of the country, from Arkansas in the south to Massachusetts in the north-east.
Supermarkets ran out of food amid a rush for supplies before the first snowflakes fell on Friday.
Washington's mayor Muriel Bowser said this was a major storm with "life and death implications".
On Friday afternoon, as the first snow fell in Washington, the National Weather Service said it could be one of the worst storms in the city's history.
Residents in the capital and surrounding suburbs in Virginia and Maryland have been warned the snowfall could eclipse the district's record of 28 inches that fell during a two-day period in 1922.
As the weather system approached the country's most populous city, New York Mayor Bill de Blasio urged residents to be ready.
New Jersey Governor Chris Christie, a Republican presidential candidate, returned from the campaign trail in New Hampshire to take charge of snow preparation.
Catholics in Washington, Baltimore, and Delaware were told by archdiocese officials that missing Mass this Sunday was excusable given the terrible conditions.
Supermarket shelves in many areas were laid bare. In Baltimore, shopper Sharon Brewington remembered how she and her daughter were left with just noodles and water when the last big snowstorm struck in 2010.
"I'm not going to make that mistake again," she said.
National Weather Service director Louis Uccellini said the system had "the potential of being an extremely dangerous storm that could affect over 50 million people".