President Barack Obama and Mitt Romney suspended their campaigning with just over a week to go before Election Day.
At the White House, the president made a direct appeal to those in harm's way: "Please listen to what your state and local officials are saying. When they tell you to evacuate, you need to evacuate. Don't delay, don't pause, don't question the instructions that are being given, because this is a powerful storm."
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 damage 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 to 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."
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.
By midafternoon, the storm was 85 miles southeast of Atlantic City, its winds at 90 mph. It had speeded up to 28 mph and had begun the turn toward the coast that forecasters had feared.
As the storm closed in, a crane dangled precariously in the wind off a 65-story luxury building in New York City, and the streets were cleared as a precaution.
The storm washed away an old section of the world-famous Atlantic City Boardwalk and left most of the city's emptied-out streets under water. All 12 casinos in the city were closed, and some 30,000 people were under orders to evacuate.
"When I think about how much water is already in the streets, and how much more is going to come with high tide tonight, this is going to be devastating. I think this is going to be a really bad situation tonight," said Bob McDevitt, president of the main Atlantic City casino workers union.
New Jersey Gov. Chris Christie, addressing those who were told to evacuate the state's barrier islands, said in his usual blunt way: "This is not a time to be a show-off. This is not a time to be stupid. This is the time to save yourself and your family."
In New York City, where 375,000 people were ordered to clear out, authorities closed the Holland Tunnel, which connects New York and New Jersey, and a tunnel between Manhattan and Brooklyn. Street grates above the subway were boarded up, but officials still worried that seawater would seep in and damage the electrical switches.
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."
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.
The major American stock exchanges closed for the day, the first unplanned shutdown since the Sept. 11 attacks in 2001. Wall Street expected to remain closed on Tuesday. 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.
Sandy, a Category 1 hurricane, was blamed for 69 deaths in the Caribbean before it began traveling northward, parallel to the Eastern Seaboard. 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, 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.
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.
Breed reported from Raleigh, N.C.; Contributing to this report were AP Science Writer Seth Borenstein in Washington; Katie Zezima in Atlantic City, N.J.; David Porter in Pompton Lakes, N.J.; Wayne Parry in Point Pleasant Beach, N.J.; and David Dishneau in Delaware.
Hurricane Sandy blog
10 amazing photos of enormous waves
Authorities use social media to keep people informed A state-by-state look at the East Coast superstorm
Hurricane Sandy is churning off the East Coast and is expected to join up with two other weather systems to create a huge and problematic storm affecting 50 million people. Here's a snapshot of what is happening or expected, state by state.
The U.S. Coast Guard rescued 14 members of a crew forced to abandon a tall ship about 90 miles off the North Carolina coast and continued to search for two other crew members. The storm lashed barrier islands and rendered several homes and businesses nearly inaccessible.
The University of Connecticut is closing Tuesday, joining a hundreds of other schools and school systems across the state. The closure includes UConn's law school and the UConn Health Center, though the John Dempsey Hospital will remain open during the storm. Power outages: 55,000.
Dover Air Force Base has relocated some aircraft in anticipation of the storm, and the Federal Emergency Management Agency has requested that the base be used as a staging area for support and supplies. Some residents of low-lying areas of the base have been ordered to evacuate.
Sandy is expected to bring snow to far southeastern Kentucky. A winter storm warning is in effect in Harlan, Letcher and Pike counties through Wednesday morning. Forecasters say snow could accumulate from 4 to 10 inches in high elevations and 1 to 3 inches in lower elevations.
Virtually all Maine public schools opened Monday but some were closing early before the heaviest rain and wind from Hurricane Sandy. State officials say the biggest concern is wind, which is expected to cause widespread power outages. The state's utilities say they have crews poised to deal with expected power outages, including some from Canada. Power outages: 5,700.
Maryland Gov. Martin O'Malley has closed the Bay Bridge because of the storm. The bridge spans the Chesapeake Bay, connecting the state's eastern and western shores. Hurricane Sandy already has caused heavy damage to a large, iconic ocean pier in the Maryland beach resort of Ocean City.
Voluntary evacuation recommendations have been issued in Scituate, Lynn, New Bedford and Plum Island. The recommendations are for just certain sections of the communities that could be affected by flooding as a result of Hurricane Sandy. A Red Cross spokeswoman said just a few people stayed at its shelters Sunday night, but she expects more people Monday night and into Tuesday. Power outages: 56,000.
Michigan utilities say high winds could cause power outages in the state and they're keeping an eye on the weather to respond to power problems. DTE Energy Co. said gusts of 50 mph Monday evening and Tuesday could affect some it its 2.1 million customers.
Gov. John Lynch has urged all drivers to be off the roads by 3 p.m. as Hurricane Sandy approaches. Lynch declared a state of emergency and directed that non-essential state workers be released from work Monday afternoon. He urged employers to consider releasing workers early. The governor has put 100 New Hampshire Guard soldiers on active duty. Power outages: 47,400.
All roads into and out of Ocean City are closed due to flooding that has cut off the popular Jersey shore resort community. Hurricane Sandy already had flooded most of Atlantic City, sweeping away an old section of the city's famed boardwalk. Power outages: 95,000.
New York City Mayor Michael Bloomberg said the city's public schools will remain closed on Tuesday after being shut down Monday. Earlier, Gov. Andrew Cuomo said the Brooklyn-Battery Tunnel and Holland Tunnel would close at 2 p.m. Monday. Airports in the metropolitan New York City area are open, but air carriers are not operating. Power outages: 263,000.
Residents of low-lying areas and along Lake Erie were told to watch for flooding; utilities are anticipating high winds that could blow down trees and poles. Snow is forecast in some areas.
Officials from the state transit agency and the Pennsylvania Turnpike have instituted speed restrictions over concerns about high winds and ordered certain vehicles, including empty trucks and motorcycles, off some highways. The National Weather Service says southeastern Pennsylvania could get winds reaching 75 mph and rainfall up to 10 inches. Power outages: 25,000.
Officials are concerned about wind driving water north up Narragansett Bay, which could create flooding in low-lying areas of the upper bay, including Providence, Warwick and Cranston. About 2,600 National Grid customers were without power, mostly in Barrington and other parts of Bristol County. Power outages: 12,000.
Snow is expected in higher elevations, where a freeze warning has been issued. High winds are expected in many areas.
Gov. Peter Shumlin declared a state of emergency to provide access to National Guard troops in a state still recovering from the devastating effects of the remnants of Hurricane Irene. Culverts and storm drainage basins in some spots have been cleared of debris. Power outages: 4,000.
A curfew is in place on Virginia's swamped Chincoteague Island. Officials say the entire 37-square-mile island is underwater, and there is no way off the island because a causeway to the mainland has been closed. The 3,500 islanders who decided to tough out Hurricane Sandy have been told to keep off the streets. Power outages: 9,500.
Taxis that originate in Washington are authorized to add an emergency flat rate of $15 per trip because of Hurricane Sandy, starting Monday. The price is supposed to expire at noon Tuesday, but can be extended if considered necessary. The capital area's transit system shut down rail service for the first time since 2003. Power outages: 2,300.
Gov. Earl Ray Tomblin declared a state of emergency Monday for West Virginia, where Sandy is expected to bring high winds and heavy rains and leave behind flooded towns and as much as 3 feet of snow on the state's highest ridge tops. Eastern parts of the state can expect to get up to 6 inches of rain. Fourteen counties are under blizzard warnings.
With waves expected to reach as high as 33 feet Tuesday on Lake Michigan, the Port of Milwaukee is taking steps to protect its docks and boats. The superstorm bearing down on the East Coast Is expected to create dangerous conditions on the Great Lakes. The National Weather Service issued gale and storm warnings for the lakes through Wednesday.