Large swaths of the US East Coast declared a state of emergency, cancelled flights and shut schools as millions braced for potentially the region's worst winter storm of the season Tuesday.
Winter Storm Stella was feared to dump up to two feet (61 centimeters) of snow in New York, combined with winds of up to 60 miles per hour (96 kilometers per hour) to cause treacherous whiteout conditions.
The forecast postponed the first meeting between President Donald Trump and German Chancellor Angela Merkel in Washington until Friday, and saw New York and New Jersey declare states of emergency.
The National Weather Service (NWS) issued a 24-hour blizzard warning from midnight Monday (0400 GMT Tuesday) for America's largest city, stretching north into Connecticut and south into New Jersey.
Additional storm warnings were posted from Maine to Virginia, south of Washington, where the National Park Service warned that the cold could wipe out up to 90 percent of the capital's beloved cherry blossoms.
In New York, UN headquarters announced it would close, inconveniencing thousands of delegates expected to attend a women's conference.
In the financial markets, much of Wall Street was expected to work from home with low trade volume anticipated, due partly to Wednesday's decision from the Federal Reserve on whether to raise interest rates.
More than 6,800 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 in New York, parts of Connecticut, Massachusetts and Rhode Island. In New York City, home to 8.4 million people, Mayor Bill de Blasio declared a state of emergency from midnight.
Trump, facing the first major weather event of his presidency after a mild winter, said he had spoken to Homeland Security and that the Federal Emergency Management Agency was ready to provide assistance.
"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 and accumulation as quick as two to four inches an hour.
"We're tracking a major storm with blizzard conditions," he said.
"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."
New York in 2016 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 paralyzed parts of the Northeast and left 18 people dead.
The Metropolitan Museum of Art, one of the biggest tourist attractions in the city, said it would close all three of its locations Tuesday.
Non-essential workers were told to stay home. In Connecticut, the governor announced a statewide travel ban as Americans across the heavily populated northeast were advised to stay off the roads.
Winter Storm Stella formed near the coast, the collision of two low pressure systems expected to dump the heaviest snow on New York, parts of Connecticut, Massachusetts, New Hampshire, Pennsylvania and Vermont.
"We're expecting it to be the worst snow of the season," NWS meteorologist Melissa Di Spigna told AFP, following winter temperatures "well above normal" this year.
The NWS cautioned that the storm could bring record low temperatures, as well as "difficult travel and power outages."
New York Governor Andrew Cuomo instructed residents to have seven to 10 days' supply of food and an emergency supply of bottled water.
In the city, the subway will be suspended above ground and express services 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.