Snow, high winds and a glacial chill hit the northeastern United States as a blast of brutal wintry weather bore down on many states and major cities, snarling air traffic.
Temperatures in New York were expected to drop to 9 degrees Fahrenheit (minus 13 degrees Celsius), according to forecasts.
Tracking system Flight Aware said that some 2,200 flights within, into or out of the United States had been cancelled.
The National Weather Service issued winter storm warnings and advisories for a huge area spanning states from Chicago trough New York, New England and even the US capital, Washington.
Severe weather was also hitting the country's Midwest, dropping a blanket of snow and cancelling flights at Chicago's O'Hare International Airport.
The northeastern winter warning was in effect in New York from Thursday evening through midday today, with forecasters predicting four to eight inches (10 to 20 centimetres) of snow and winds that could reach up to 35 miles (56 kilometres) per hour.
The National Weather Service said blizzard conditions were possible for eastern Long Island and the coast of Massachusetts.
"Bitter cold will move into the Midwest and East following the storm," it warned.
In the Big Apple, where thick flakes were falling Thursday evening, the storm will serve as a first test for the city's new mayor, Bill de Blasio, who assumed his post Wednesday.
De Blasio said the city had "laser" focus as it braced for what was to come.
"We are ready," he said.
He urged residents to stay indoors and use public transportation if they must get around. But, he warned, delays were to be expected.
"Please, starting this evening, stay inside. If you don't need to go out, don't go out," de Blasio said.
New York Governor Andrew Cuomo activated the State Emergency Operations Centre and also urged people to use mass transit, warning of possible highway closures due to inclement weather.
In neighbouring New Jersey, Governor Chris Christie declared a state of emergency in anticipation of what was to come.
Connecticut Governor Dannel Malloy, meanwhile, ordered state employees to leave work early on Thursday to alleviate the evening commute. Workers were not expected back at their desks until mid-morning.
