Forecasters expected the monster hurricane to make a westward lurch and aim for New Jersey, blowing ashore Monday night or early Tuesday and combining with two other weather systems to create an epic superstorm.
Its projected path put New York City and Long Island in the danger zone for a huge surge of seawater made more fearsome by high tides and a full moon.
"This is the worst-case scenario," said Louis Uccellini, environmental prediction chief for the National Oceanic and Atmospheric Administration.
Because the storm is so big, with tropical storm-force winds extending almost 500 miles from its center, it could upend daily life for big cities and small towns alike across the Northeast — including Washington, Baltimore, Philadelphia, New York and Boston — and as far west as the Great Lakes. Up to 3 feet of snow was forecast for the West Virginia mountains.
Millions of people in the storm's path stayed home from work. Subways, buses and trains shut down, and more than 7,000 flights in and out of the East were canceled, snarling travel around the globe. Hundreds of thousands of people were under orders to flee the coast, including 375,000 in lower Manhattan and other parts of New York City, but authorities warned that the time to get out was short or already past.
"I think this one's going to do us in," said Mark Palazzolo, who boarded up his bait-and-tackle shop in Point Pleasant Beach, N.J., with the same wood he used in past storms, crossing out the names of Hurricanes Isaac and Irene and spray-painting "Sandy" next to them.
"I got a call from a friend of mine from Florida last night who said, 'Mark, get out! If it's not the storm, it'll be the aftermath. People are going to be fighting in the streets over gasoline and food.'"
President Barack Obama declared emergencies in Massachusetts, Connecticut, Rhode Island, New York, New Jersey and Pennsylvania, authorizing federal relief work to begin well ahead of time. He promised the government would "respond big and respond fast" after the storm hits.
"My message to the governors as well as to the mayors is anything they need, we will be there, and we will cut through red tape," Obama said. "We are not going to get bogged down with a lot of rules."
Sandy, a Category 1 hurricane with sustained winds of 85 mph early Monday, was blamed for 65 deaths in the Caribbean before it began traveling northward, parallel to the Eastern Seaboard. As of 8 a.m. Monday, it was centered about 310 miles southeast of New York City, moving to the north at 20 mph, with hurricane-force winds extending an extraordinary 175 miles from its center.
About 90 miles off Cape Hatteras, N.C., the Coast Guard rescued 14 crew members by helicopter from a replica of the 18th-century tall ship made famous in the movie "Mutiny on the Bounty." The Coast Guard searched for two other crew members.
The rescued had donned survival suits and life jackets and boarded two lifeboats after the ship began taking on water. They were plucked from 18-foot seas just before sunrise.
Maryland Gov. Martin O'Malley said a fishing pier in the beach resort of Ocean City, not far from a popular boardwalk and amusement park, was "half-gone." The area had been ordered evacuated on Sunday.
Water was already a foot deep on the streets of Lindenhurst, N.Y., along the southern edge of Long Island, and the canals around the island's Great South Bay were bulging two hours before high tide. Gale-force winds blew overnight over coastal North Carolina, southeastern Virginia, the Delmarva Peninsula and coastal New Jersey.
Forecasters warned that New York City and Long Island could be on the dangerous northeastern edge of the tempest and bear the worst of the storm surge — a wall of seawater up to 11 feet high that could swamp lower Manhattan, flood subway tunnels and cripple the network of electrical and communications lines that are vital to the nation's financial center.
The major American stock exchanges closed for the day, the first unplanned shutdown since the Sept. 11 attacks in 2001. The floor of the NYSE, typically bustling with traders on a Monday morning, fell within the city's mandatory evacuation zone. The United Nations canceled all meetings at its New York headquarters.
New York called off school for the city's 1.1 million students, and the more than 5 million people who depend on its transit network every day were left without a way to get around. Most planned to stay inside anyway.
"If you don't evacuate, you are not only endangering your life, you are also endangering the lives of the first responders who are going in to rescue you," Mayor Michael Bloomberg warned. "This is a serious and dangerous storm."
New Jersey Gov. Chris Christie was typically blunt: "Don't be stupid. Get out."
The storm bore down barely a week before the presidential election. Wary of being seen as putting political pursuits ahead of public safety, Obama and Republican nominee Mitt Romney reshuffled their campaign plans.
In Virginia, one of the most competitive states, election officials eased absentee voting requirements for those affected by the storm. Three other closely contested states, New Hampshire, North Carolina and Ohio, were within Sandy's reach. Early voting was canceled Monday in Maryland and Washington, D.C., both reliably Democratic.
After hooking inland, Sandy was expected to collide with a wintry storm moving in from the west and cold air streaming down from the Arctic. Forecasters said the combination could bring close to a foot of rain in places, a potentially lethal storm surge of 4 to 11 feet across much of the region, and punishing winds that could cause widespread power outages that last for days.
Craig Fugate, chief of the Federal Emergency Management Agency, said FEMA teams were deployed from North Carolina to Maine and as far inland as West Virginia, bringing generators and basic supplies that will be needed in the storm's aftermath.
"I have not been around long enough to see a hurricane forecast with a snow advisory in it," Fugate told NBC's "Today" show.
Pennsylvania's largest utilities brought in hundreds of line-repair and tree-trimming crews. In New Jersey, where utilities were widely criticized last year for slow responses after the remnants of storms Irene and Lee, authorities promised a better performance. Hundreds of homes and businesses were already without electricity early Monday.