National Weather Service blizzard and winter storm warnings were in effect for the region including New York, Pennsylvania, New Jersey and Connecticut, with forecasts for up to 2 feet (60 cm) of snow by early Wednesday and temperatures 15 to 30 degrees below normal for this time of year.

Some 50 million people along the Eastern Seaboard were under storm or blizzard warnings and watches.

“If you must go out, do so for as limited time period as possible … but the best thing to do is stay in,” New York Mayor Bill de Blasio said on Monday.

Above-ground subway service was suspended as transit officials in the New York metro area warned that more bus and train routes might be suspended throughout the day.

“It’s a good day to stay home,” said New York Governor Andrew Cuomo on CBS Radio. “It is going to be a dangerous, dangerous situation.”

The Port Authority of New York and New Jersey prepared hundreds snow-clearing vehicles at the three major New York area airports. Thousands of tons of salt and sand were prepared for airport roads, parking lots, bridges and tunnels.

Airlines canceled more than 5,800 flights across the United States, according to tracking service FlightAware.com. The airports with the most cancelations were Newark in New Jersey, LaGuardia in New York and Boston Logan International Airport.

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

Delta Air Lines (DAL) canceled 800 flights for Tuesday for New York, Boston and other northeast airports. United Airlines (UAL) 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.

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

“When this thing hits, it’s going to hit hard and it’s going to put a ton of snow on the ground in a hurry,” Massachusetts Governor Charlie Baker said, urging people to consider working from home if they could.

New York City public schools—the largest U.S. school system—canceled classes on Tuesday. Districts in Boston, Fairfax County, Virginia, and Philadelphia were also shut.

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

Boston Braces for Snow

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, D.C.

Boston was braced for up to a foot of snow, which forecasters warned would fall quickly during the storm’s peak. Washington D.C., a city which functions badly with even small amounts of snow, was expecting 5 inches (13 cm) and twice that in outlying areas.

Snow fall will 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.

“Visibilities will become poor with whiteout conditions at times,” it said.

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.

The United Nations headquarters said it would close on Tuesday, but the New York Stock Exchange vowed to remain open.