By Daniel Trotta and Scott Malone

NEW YORK/BOSTON (Reuters) – Snow piled up rapidly in parts of the northeastern United States on Tuesday as a blizzard began blowing in, with residents being advised to stay at home, airlines grounding flights and schools canceling classes.

The National Weather Service (NWS) warned some 50 million people from Pennsylvania to Maine of a “rapidly intensifying nor’easter” that was unusual for so late in the winter. Some could expect to find themselves surrounded by up to 2 feet (60 cm) of snow by early Wednesday, the federal agency predicted.

Governors in New York, New Jersey, Pennsylvania and Virginia declared states of emergency.

New York City was expected to escape the worst of it after the NWS withdrew its blizzard warning for the city on Tuesday morning, replacing it with a mere “winter weather advisory.” The service sharply reduced its snowfall forecast for the city to between 4 and 8 inches (10 and 20 cm).

Still, city life already was disrupted with many New Yorkers already planning to stay home with hard-won groceries picked up from crowded stores the night before.

New York Governor Andrew Cuomo suspended above-ground portions of the city’s subway service and said the Metro-North commuter service to the suburbs would shut down at noon. Transit officials warned that more bus and train routes might be suspended throughout the day.

“Normally, with the geography of New York, we normally have it on the east side or the west side. But this is statewide,” Cuomo told MSNBC in an interview.

“We’ve been through this a number of times so we’re prepared for it. Airports are basically closed … Government is basically closed, schools are basically closed, so there’s no real reason to be on the roads and we made that clear yesterday.”

Some 2,000 members of the National Guard and 5,000 plows were deployed across the state, Cuomo said.

Workers clear frozen precipitation from a walkway at the U.S. Capitol in Washington, U.S., March 14, 2017. REUTERS/Jonathan Ernst

AIR TRAFFIC SNARLED

Airlines canceled about 5,500 flights across the United States, according to tracking service FlightAware.com. The airports with the most cancellations were Newark in New Jersey, LaGuardia in New York and Boston Logan International Airport.

American Airlines <AAL.O> canceled all flights into New York’s three airports – Newark, LaGuardia and John F. Kennedy International Airport – and JetBlue Airways <JBLU.O> reported extensive cancellations.

Delta Air Lines <DAL.N> canceled 800 flights for Tuesday for New York, Boston and other northeast airports. United Airlines <UAL.N> said it would have no operations at Newark or LaGuardia.

“We’re keeping a close eye on things and depending on how things go, will plan to ramp back up Wednesday morning,” United said in a statement.

New York City public schools – the largest U.S. school system – canceled classes on Tuesday as did schools in the Washington, D.C., area, Boston, Philadelphia and northern New Jersey.

Federal agencies in Washington said they were opening three hours later than normal on Tuesday.

The storm comes near the end of an unusually mild winter along much of the East Coast, with below-normal snowfalls in cities such as New York City and Washington.

Boston was braced for up to a foot of snow, which forecasters warned would fall quickly during the storm’s peak. The double-murder trial in Boston of former New England Patriots star Aaron Hernandez was suspended for the day because of the weather.

Washington, a city that functions badly with even small amounts of snow, was expecting 5 inches (13 cm) and twice that in outlying areas.

Snow fall was to be heavy at times with as much as 4 inches an hour expected to fall with winds reaching up to 60 mph (100 kph) in parts of the northeast, the National Weather Service warned.

Coastal flood warnings were also in effect for several parts of the region as a storm surge is expected during high tide on Tuesday, the weather service said.

German Chancellor Angela Merkel, who was due to meet President Donald Trump in Washington on Tuesday, postponed her trip until Friday, the White House said.

Shelves are seen scarce with bread at a Trader Joe’s grocery store ahead of a fast-moving winter storm expected to hit the northeastern United States, in the borough of Manhattan in New York, U.S., March 13, 2017. REUTERS/Shannon Stapleton

(Additional reporting by Brendan O’Brien in Milwaukee, Laila Kearney and Jonathan Allen in New York and Scott Malone in Boston; Editing by Louise Ireland and Bill Trott)