Airlines grounded hundreds of flights today along the north-east corridor in anticipation of the storm, affecting major airports including New York's JFK and Newark.
Airlines said more cancellations were likely as the storm progressed. Travel misery began a day earlier in parts of the South, where a rare white Christmas came with reports of dozens of car crashes.
In Washington transport officials pre-treated roads and readied 200 salt trucks and other pieces of equipment to fight the 6in or more expected to fall in the Mid-Atlantic region.
The north-east is expected to get the brunt of the storm. Forecasters issued a blizzard warning for New York City for today and tomorrow. A blizzard warning was also in effect for Rhode Island and most of eastern Massachusetts including Boston. A blizzard warning is issued when snow is accompanied by sustained winds or gusts over 35mph.
By early today, Maryland, Virginia and North Carolina declared states of emergency.
"We're urging extreme caution in travel. Try to get home early and if you don't have to travel don't go," Virginia Governor Bob McDonnell told The Weather Channel.
Most air carriers were waiving fees for one-time changes in affected areas and urging passengers to make changes through their websites.
The monster storm is the result of a low pressure system that will intensify off the North Carolina coast and strengthen into a major storm as it moves north-east, according to the National Weather Service.
The system gave the Carolinas their first white Christmas in decades. Columbia, South Carolina, had its first significant Christmas snow since weather records were first kept in 1887.
The North Carolina Highway Patrol said late yesterday that most of the roads in and around Asheville were either covered or partially covered with snow and ice. Emergency management spokeswoman Julia Jarema said troopers in the two dozen western-most counties answered 350 calls in 18 hours yesterday.
Major airlines cancelled flights in the storm's path today. Continental Airlines cancelled 250 departures from Newark Liberty International Airport outside New York City. United Airlines cancelled dozens of departures from Newark, Philadelphia, New York's LaGuardia and JFK, Boston and other airports. AirTran and Southwest Airlines also cancelled flights, mostly in or out of Washington Dulles, Baltimore and Newark.
Delta Air Lines spokesman Kent Landers said the airline cancelled about 850 mainline and regional flights.
Mary Sanderson at American Airlines said flights through Washington, Baltimore and Philadelphia would probably be cancelled later today, with late starts expected on Monday morning.
In London, Heathrow airport was open today, but warned on its website of flight cancellations and delays due to bad weather in the US. Fifteen British Airways flights out of Heathrow to the US were cancelled, including ones to New York's JFK airport, Newark, Boston, Philadelphia, Baltimore and Washington Dulles airport.
In Paris, five flights leaving for JFK from Charles de Gaulle airport were cancelled today, along with three flights to Newark and one bound for Philadelphia.
At Washington's Reagan National Airport, Rob Kotlarz, of Surrey, was trying to fly his children Sofia and Stefan to Orlando, Florida, to visit Disney World.
"Of all the flights to Orlando today the only one that was cancelled was our 3.10pm ... and the US Airways helpline was impossible," he said.
"But we were expecting America to show us how to handle weather. We showed up seven hours early so we could be here. In this digital age why can't an airline handle it better?"