(CNN) — A Nor’easter is dumping snow and pushing winds up the US East Coast — the beginnings of a monster storm that has placed about 18 million people under a blizzard warning.

So far, nearly 7,700 US flights have been canceled through Wednesday and thousands of schools have closed. Winter storm warnings and watches have been hoisted over a region stretching from West Virginia into Maine.

Local and state authorities warned residents to be prepared and to avoid unnecessary travel as winds in some coastal areas could hit 50 mph to 60 mph, reducing visibility to zero.

A blizzard warning — cautioning that high winds will combine with snow for poor visibility — was in effect Tuesday morning for parts of Pennsylvania, New York, New Jersey and the six New England states.

Weather models Tuesday morning showed that the heaviest snow, perhaps more than 2 feet, could hit northeastern Pennsylvania, New York’s Hudson Valley and parts of Vermont and New Hampshire.

Among major developments:

— Snow is falling Tuesday morning in Washington DC up through Philadelphia, and New York City.

— About 18 million people are under a blizzard warning and millions more are under a winter storm warning.

— States of emergency have been declared in Maryland, Virginia, New York, New Jersey and Pennsylvania.

— Boston, Baltimore, Philadelphia and New York City school districts will be closed Tuesday, along with many government offices.

— Airlines canceled more than 6,100 US flights scheduled for Tuesday and Wednesday, according to Flightaware.com. That’s on top of 1,658 flights canceled Monday.

— New York City: A blizzard warning initially issued here was canceled Tuesday morning, but the city still could get as much as 8 inches of snow Tuesday, with higher amounts possible to the north and west. About 4 inches had fallen at Central Park by 8 a.m. ET. Snow may mix with sleet or rain; wind gusts as strong as 45 mph are possible.

— Parts of New York City, Long Island and southern Connecticut: Minor to moderate coastal flooding is possible around high tide on Tuesday afternoon, the National Weather Service said.

— Philadelphia could see freezing rain and sleet Tuesday morning before getting as much as 10 inches of snow in the afternoon and into Wednesday. Wind gusts up to 40 mph are possible.

— Parts of western Massachusetts could receive 24 inches or more, along with powerful winds. Coastal Massachusetts could feel wind gusts of up to 60 mph, and high storm surges are possible.

— The Boston area could get as much as 12 inches of snow and sleet; snow is due to fall into the late afternoon, followed by rain and sleet. A snow emergency was declared in the city Tuesday morning, meaning vehicles will be towed if they are parked on roads that are marked as snow emergency arteries.

— In Connecticut, a statewide travel ban went into effect Tuesday at 5 a.m. ET. “Wherever you are at sunrise Tuesday morning, expect to remain there throughout the remainder of the storm and into (Tuesday) night,” Connecticut Gov. Dannel Malloy said.

— In Virginia, the Coast Guard closed the Port of Virginia on the harbor at Hampton Roads. In a news release Monday night, the agency said 50 mph winds predicted from the pending storm could create hazardous conditions that would make it difficult for Coast Guard units to reach distressed mariners.

Travel warnings, snow and sleet

Warnings to use caution came from public officials up and down the East Coast — including the President.

“Everyone along the east coast be safe and listen to local officials as a major winter storm approaches,” President Donald Trump tweeted.

Federal agencies in the Washington area will open three hours late Tuesday; employees have the option of taking unscheduled leave or teleworking, according to the US Office of Personnel Management.

In addition to show hazards, the region is expecting downed power lines and service interruptions.

“This should be a very serious blizzard, one that everyone should take seriously,” New York Mayor Bill de Blasio said.

In Massachusetts, its governor said the state expects sleet, rain and extremely cold temperatures along the coast.

“This is going to be a lot of snow and it’s going to be a mess,” Baker said.

This storm system already hit the Midwest, claiming two lives in Wisconsin. The victims — both men — died in separate weather-related activities, the Milwaukee County Medical Examiner reported.

One man, 76, was operating a snow blower before he died; the second man, 64, was shoveling snow, investigator Jenni Penn said. Both were cardiac-related deaths, Penn said.