The stage was set for a possibly historic "nor'easter" that would affect an area from central New Jersey to the Canadian border from today to Wednesday, the National Weather Service said.
Officials in Boston, New York, Philadelphia and Washington urged residents to stay home as they prepared for a storm that could dump up to three feet (about a metre) of snow in some areas.
"My message to all New Yorkers is to prepare for something worse than we have seen before."
"Take every precaution, now is the time to get ready for this extreme weather," de Blasio said. "Don't underestimate the storm."
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The US Weather Channel referred to the cold blast as a "possibly historic" winter storm, as airlines cancelled more than 1,800 flights early today as the weather system neared, according to flightaware.Com.
Some airlines waved change fees as major delays and widespread cancellations were anticipated.
"Many of the major metropolitan areas will be affected anywhere from Philadelphia through New York City and into Boston," it added.
Blizzard warnings were in effect along the coast from central New Jersey to the Canadian border.
People were scrambling to pick up storm staples such as shovels, road salt and ice scrapers.
In downtown Manhattan, an employee at a Home Depot hardware store crammed with pre-storm shoppers shot and killed his boss before turning the gun on himself, police said. The motive was not immediately clear.
New York city-area Port Authority employees have been ordered to work 12-hour shift starting today to prepare for the onslaught, he added.
The weather service said 18 to 24 inches (45 to 60 centimetres) could fall from southeastern New York to coastal New England.