NEW YORK (AP) - The Philadelphia-to-Boston corridor of more than 35 million people began shutting down Monday as a monster storm that could unload a paralyzing 1 to 3 feet of snow swirled into the Northeast. Snow was blowing sideways with ever-increasing intensity in New York City by midafternoon as flurries began in Boston. Forecasters said the storm would build into a blizzard, and the brunt of it would hit Monday evening and into Tuesday. More than 5,800 flights in and out of the Northeast were canceled, and many of them may not take off again until Wednesday. Schools and businesses let out early. State government offices closed. And cities mobilized snowplows and salt spreaders to deal with a dangerously windy blast that could instantly make up for what has been a largely snow-free winter in the urban Northeast. All too aware that big snowstorms can make or break politicians, governors and mayors moved quickly to declare emergencies and order the shutdown of highways, streets and mass transit systems - perhaps for days - to prevent travelers from getting stranded and to enable plows and emergency vehicles to get through. "It is not a regular storm," New York Mayor Bill de Blasio warned in ordering city streets closed to all but emergency vehicles beginning at 11 p.m. "What you are going to see in a few hours is something that hits very hard and very fast." Boston is expected to get 2 to 3 feet, New York 1½ to 2 feet, and Philadelphia more than a foot. The National Weather Service issued a blizzard warning for a 250-mile swath of the region, meaning heavy, blowing snow and potential whiteout conditions. On the snowy Metro-North commuter train platform in White Plains, New York, postal worker Peter Hovey said he will be playing it safe when he has to deliver packages on Tuesday. "If you're telling me the trains might not run tomorrow, I'm telling you this: I'm not driving," he said. "It's going to be ridiculous out there, frightening." In Hartford, Connecticut, Frank Kurzatkowski stopped for gas and said he also filled several five-gallon buckets of water at his home in case the power went out and his well pump failed. "I've got gas cans filled for my snowblowers," he said. "I have four-wheel-drive." Supermarkets and hardware stores did a brisk trade as light snow fell in New Jersey. Nicole Coelho, 29, a nanny from Lyndhurst, New Jersey, was preparing to pick up her charges early from school and stocking up on macaroni and cheese, frozen pizzas and milk at a supermarket. She also was ready in case of a power outage. "I'm going to make sure to charge up my cellphone, and I have a good book I haven't gotten around to reading yet," she said. About half of all flights out of New York's LaGuardia Airport were called off Monday, and about 60 percent of flights heading into the airport were scratched. Boston's Logan Airport said there would be no flights after 7 p.m. Monday. Coastal residents braced for a powerful storm surge and the possibility of damaging flooding and beach erosion, particularly in New Jersey and on Cape Cod in Massachusetts. Officials in New Jersey shore towns warned people to move their cars off the streets and away from the water. Utility companies across the region put additional crews on standby to deal with anticipated power outages from high winds. The storm posed one of the biggest tests yet for Massachusetts Gov. Charlie Baker, who has been in office for less than three weeks. He warned residents to prepare for power outages and roads that are "very hard, if not impossible, to navigate." Wind gusts of 75 mph or more were possible for coastal areas of Massachusetts, and up to 50 mph farther inland, forecasters said. The storm interrupted jury selection in the Boston Marathon bombing case and forced a postponement in opening statements in the murder trial of former NFL star Aaron Hernandez in Fall River, Massachusetts. New York Gov. Andrew Cuomo declared a state of emergency and urged commuters to stay home on Monday, warning that roads could be closed before the evening rush hour, even major highways such as the New York Thruway and the Long Island Expressway. Similarly, Connecticut Gov. Dannel P. Malloy ordered a travel ban on his state's highways, while officials in other states asked residents to avoid going anywhere unless it is necessary. The Washington area was expecting only a couple of inches of snow. But the House postponed votes scheduled for Monday night because lawmakers were having difficulty flying back to the nation's capital after the weekend. On Wall Street, the New York Stock Exchange said it will stay open and operate normally on Monday and Tuesday. A tractor-trailer jackknifed, and a beer truck crashed into the median on Interstate 81 near Harrisburg, Pennsylvania, during the morning commute. No injuries were reported. The Super Bowl-bound New England Patriots expected to be out of town by the time the storm arrived in Boston. The team planned to leave Logan Airport at 12:30 p.m. Monday for Phoenix, where the temperature will reach the high 60s. Associated Press writers Dave Collins and Pat Eaton-Robb in Hartford, Connecticut; David Porter in Lyndhurst, New Jersey; Jim Fitzgerald in White Plains, N.Y.; Bruce Shipkowski in Trenton, New Jersey; Deepti Hajela and Verena Dobnik in New York; Albert Stumm in Philadelphia; and Marcy Gordon and Darlene Superville in Washington contributed to this report.