This NASA satellite handout image shows storm activity in eastern US on March 13. Photograph: (AFP)
A 24-hour blizzard warning has been issued for New York, stretching north into Connecticut and south into New Jersey
Large swaths of the US East Coast declared a state of emergency, cancelled flights and shut schools as millions braced for potentially the worst winter storm of the season with up to two feet of snow forecast to fall.
Winter Storm Stella is expected to begin overnight with accumulation becoming most intense Tuesday morning, combined with winds of up to 60 miles per hour (96 kilometers per hour) to cause treacherous whiteout conditions.
The alarming forecast forced the postponement of the first meeting between President Donald Trump and German Chancellor Angela Merkel in Washington from Tuesday until Friday.
New York and New Jersey declared states of emergency.
The National Weather Service issued a 24-hour blizzard warning from midnight Monday (0400 GMT Tuesday) for New York, America's financial capital and largest city, stretching north into Connecticut and south into New Jersey.
Additional winter storm warnings were posted from southern Maine to Virginia, south of Washington, where the National Park Service warned that the blustery weather could wipe out up to 90 per cent of the city's famed cherry blossoms.
In New York, UN headquarters will close and Wall Street largely expected to work from home with low trade volume anticipated, if also due to Wednesday's decision from the Federal Reserve on whether to raise interest rates.
More than 6,500 US flights were cancelled for Monday and Tuesday, with airports in New York, Boston, Baltimore, Washington and Philadelphia hardest hit, according to the tracking service FlightAware.
Schools will close Tuesday in New York, Providence, Rhode Island and in towns across Connecticut and Massachusetts. In New York City, home to 8.4 million people, Mayor Bill de Blasio declared a state of emergency from midnight.
Non-essential state workers were told to stay home. In Connecticut, the governor announced a statewide travel ban from 5 am as Americans across the heavily populated northeast were advised to stay off the roads.
Trump, facing the first major weather event of his presidency after a mild winter, said Monday he had spoken to Homeland Security and that the Federal Emergency Management Agency was ready to provide assistance if necessary.
"Everybody in government is fully prepared and ready," he said. "Let's hope it's not going to be as bad as some people are predicting. Usually it isn't."
But de Blasio wasn't taking any chances, with 16 to 24 inches (41 to 61 centimeters) of snow forecast for New York and expected to fall as quickly as two to four inches an hour.
"We're tracking a major storm with blizzard conditions," said de Blasio.
"High end could be as much as 24 inches which would therefore put this in the category of one of the biggest snowstorms in recent memory," he said.
New York last year experienced the biggest snowstorm in the city's history with a record 27.3 inches falling in Central Park in 24 hours. Winter Storm Jonas paralysed parts of the Northeast and left 18 people dead.
This week's Winter Storm Stella formed near the coast, the collision of two low pressure systems expected to dump snow on a wide area home to tens of millions of Americans from the central Appalachian Mountains to New England.
Worst of season
The heaviest snow is expected to wallop New York, parts of Connecticut, Massachusetts, New Hampshire, Pennsylvania and Vermont.
"We're expecting it to be the worst snow of the season," National Weather Service meteorologist Melissa Di Spigna told AFP, following winter temperatures "well above normal" this year.
The National Weather Service cautioned that the storm could bring record-low temperatures, as well as "difficult travel and power outages."
Temperatures on Monday were already icy, with afternoon highs hovering around the freezing point.
Around 5,000 flights within, into or out of the United States have been cancelled for Tuesday, mostly along the East Coast, according to FlightAware.
New York State Governor Andrew Cuomo instructed residents to have seven to 10 days' supply of food and an emergency supply of bottled water.
In New York, the subway will be suspended above ground at 4am (0800 GMT) and express subway service will end at midnight, with bus and commuter rail services into Long Island and north of the city also likely to be suspended.
In Washington, the Metro is planning to operate on a Saturday schedule and Metrobus will start the day on a "severe" modified schedule.