The monster hurricane was expected to make a westward lurch and aim for New Jersey, blowing ashore Monday night and combining with two other weather systems — a wintry storm from the west and cold air rushing in from the Arctic — to create an epic superstorm.
Authorities warned that New York City and Long Island could get the worst of the storm surge — an 11-foot onslaught of seawater that could swamp lower Manhattan, flood the subways and cripple the underground network of electrical and communications lines that are vital to the nation's financial capital.
Because of Sandy's vast reach, with tropical storm-force winds extending almost 500 miles from its center, other major cities across the Northeast — Washington, Baltimore, Philadelphia and Boston — also prepared for the worst.
"The days ahead are going to be very difficult," Maryland Gov. Martin O'Malley said. "There will be people who die and are killed in this storm."
By late morning, the storm had strengthened to 90 mph and had already knocked out power to tens of thousands of people. Sandy was about 200 miles southeast of Atlantic City, N.J., where the emptied-out streets were mostly under water and where an old section of the historic boardwalk broke up and washed away.
Authorities moved to close the Holland Tunnel, which connects New York and New Jersey, and a tunnel between Manhattan and Brooklyn. Street grates above the New York subway were boarded up, but officials worried that seawater would seep in and damage the electrical switches.
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.
Sheila Gladden evacuated her home in Philadelphia's flood-prone Eastwick neighborhood and headed to a hotel.
"I'm not going through this again," said Gladden, who had 5 1/2 feet of water in her home after Hurricane Floyd in 1999.
"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 and Republican Mitt Romney called off their campaign events at the very height of the presidential race, with just over a week to go before Election Day. And early voting was canceled Monday in Maryland and Washington, D.C.
The president 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, was blamed for 69 deaths in the Caribbean before it began traveling northward, parallel to the Eastern Seaboard. As of 11 a.m., it was moving at 18 mph, with hurricane-force winds extending an extraordinary 175 miles from its center.
Forecasters said the combined Frankenstorm 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. Up to 3 feet of snow was forecast for the West Virginia mountains.
About 90 miles off Cape Hatteras, N.C., the Coast Guard rescued 14 crew members by helicopter from the HMS Bounty, a replica 18th-century sailing ship that sank in the storm. The Coast Guard searched for two other crew members. The ship was built for the 1962 Marlon Brando film "Mutiny on the Bounty."
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.
O'Malley, the Maryland governor, 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.
In the morning, water was already splashing over the seawalls at the southern tip of Manhattan and had matched the levels seen during Hurricane Irene in August 2011. Still, people were out jogging, walking their dogs and even taking children out in strollers amid gusts of wind.
"We're high up enough, so I'm not worried about flooding," said Mark Vial, who was pushing his 2-year-old daughter, Maziyar, in a stroller outside their building, where they live on the 15th floor. "There's plenty of food. We'll be OK."
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 on both Monday and Tuesday 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.
"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."
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.