Sandy knocked out power to at least 3.1 million people across the East, and New York City's main utility said large sections of Manhattan were plunged into darkness. Water pressed into the island from three sides.
Just before the storm center reached land, forecasters stripped it of hurricane status, but the distinction was purely technical, based on its shape and internal temperature. It still packed hurricane-force wind, and forecasters were careful to say it remained every bit as dangerous to the 50 million people in its path.
As the storm closed in, it smacked the boarded-up big cities of the Northeast corridor - Washington, Baltimore, Philadelphia, New York and Boston - with stinging rain and gusts of more than 85 mph. It also converged with a cold-weather system that turned it into a superstorm, a monstrous hybrid consisting not only of rain and high wind but snow.
Sandy made landfall at 8 p.m. near Atlantic City, which was already mostly under water and saw a piece of its world-famous Boardwalk washed away earlier in the day.
The effects of the storm are being felt in the Midwest. Chicago OEMC announced several precautions at a news conference Monday afternoon, including the closure of the Ferris wheel and all outside concessions at Navy Pier. It was announced that preparations are in place to close Lake Shore Drive, if necessary. City officials are warning everyone to stay away from the lake because of the threat of high waves.
The lakefront trail will be closed Monday starting at 11 p.m. It will be shut down from North Avenue to Ohio and that area could be extended. The CTA is also prepared to reroute buses if needed due to the high waves and wind.
Authorities in several states were taking unprecedented actions to protect people from the massive superstorm. ABC7 Chicago reporter Ben Bradley is covering the storm from Cape May, New Jersey -- about 75 miles south of Philadelphia.
Curtis Bashaw, a Wheaton College alum, is now riding out the storm in the hotel he owns in Cape May, New Jersey. It stands within sight of the water threatens to engulf half of the entire town.
"We definitely feel like the landfall has happened and we're still here and we're grateful for that," said Bashaw. "Chicago winters are not exactly the nicest winters but when you have a cyclone or hurricane churning up the ocean within site of your building; it definitely makes your heart stop a bit."
"Property can be replaced - lives can't. That's what we're focused on is preventing injuries," said Ed Mahaney, Cape May, New Jersey, mayor.
Most people are off the island.
"Fifteen thousand were here last weekend, we're down to 500 now," Mahaney said.
The time for boarding up has passed. Still the family-owned hardware store that's been in Cape May for a century remains open in case emergency crews need supplies.
"Most people think we're crazy but that's probably why we've been here 116 years!" said Glenn Mcbrearty, Cape May hardware store owner.
The Congress Hall hotel is even older, and Curtis Bashaw hopes better situated to withstand Sandy's punch.
"This is going to be a 50, 60, 70 year storm," he said.
Authorities reported a record surge 13 feet high at the Battery at the southern tip of Manhattan, from the storm and high tide combined.
In an attempt to lessen damage from saltwater to the subway system and the electrical network beneath the city's financial district, New York City's main utility cut power to about 6,500 customers in lower Manhattan. But a far wider swath of the city was hit with blackouts caused by flooding and transformer explosions.
The subway system was shut down Sunday night, and the stock markets never opened at all Monday. They are likely to be closed Tuesday as well.
The surge hit New York City hours after a construction crane atop a luxury high-rise collapsed in the wind and dangled precariously 74 floors above the street. Forecasters said the wind at the top the building may have been close to 95 mph.
As the storm drew near, airlines canceled more than 12,000 flights, disrupting the plans of travelers all over the world.
Storm damage was projected at $10 billion to $20 billion, meaning it could prove to be one of the costliest natural disasters in U.S. history.
Ten deaths were reported in New Jersey, New York, West Virginia, Pennsylvania and Connecticut. Some of the victims were killed by falling trees. At least one death was blamed on the storm in Canada.
President Barack Obama and Republican challenger Mitt Romney canceled their campaign appearances at the very height of the race, with just over a week to go before Election Day. The president pledged the government's help and made a direct plea from the White House to those in the storm's path.
"When they tell you to evacuate, you need to evacuate," he said. "Don't delay, don't pause, don't question the instructions that are being given, because this is a powerful storm."
Sandy, which killed 69 people in the Caribbean before making its way up the Atlantic, began to hook left at midday toward the New Jersey coast.
New Jersey Gov. Chris Christie said people were stranded in Atlantic City, which sits on a barrier island. He accused the mayor of allowing them to stay there. With the hurricane roaring through, Christie warned it was no longer safe for rescuers, and advised people who didn't evacuate the barrier islands to "hunker down" until morning.
"I hope, I pray, that there won't be any loss of life because of it," he said.
While the hurricane's 90 mph winds registered as only a Category 1 on a scale of five, it packed "astoundingly low" barometric pressure, giving it terrific energy to push water inland, said Kerry Emanuel, a professor of meteorology at MIT.
And the New York metropolitan apparently got the worst of it, because it was on the dangerous northeastern wall of the storm.
"We are looking at the highest storm surges ever recorded" in the Northeast, said Jeff Masters, meteorology director for Weather Underground, a private forecasting service. "The energy of the storm surge is off the charts, basically."
Hours before landfall, there was graphic evidence of the storm's power.
A construction crane atop a luxury high-rise in New York City collapsed in the wind and dangled precariously 74 floors above the street. Forecasters said the wind at the top the building may have been close to 95 mph.
Off North Carolina, a replica of the 18th-century sailing ship HMS Bounty that was built for the 1962 Marlon Brando movie "Mutiny on the Bounty" went down in the storm, and 14 crew members were rescued by helicopter from rubber lifeboats bobbing in 18-foot seas. Another crew member was found hours later but was unresponsive. The captain was missing.
At Cape May, water sloshed over the seawall, and it punched through dunes in other seaside communities. Sandy also tore away an old section of Atlantic City's historic boardwalk.
"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," said Bob McDevitt, president of the main Atlantic City casino workers union. "I think this is going to be a really bad situation tonight."
In Maryland, at least 100 feet of a fishing pier at the beach resort of Ocean City was destroyed, and Gov. Martin O'Malley said there would be devastating flooding from the swollen Chesapeake Bay.
"There will be people who die and are killed in this storm," he said.
At least half a million people had been ordered to evacuate, including 375,000 from low-lying parts of New York City, and by the afternoon authorities were warning that it could be too late for people who had not left already.
Sheila Gladden evacuated her home in Philadelphia's flood-prone Eastwick neighborhood, which took on 5½ feet of water during Hurricane Floyd in 1999, and headed for a hotel.
"I'm not going through this again," she said.
Those who stayed behind had few ways to get out. Not only was the subway shut down, but the Holland Tunnel connecting New York to New Jersey was closed, as was a tunnel between Brooklyn and Manhattan, and the city planned to shut down the Brooklyn Bridge, the George Washington, the Verrazano-Narrows and several other spans because of high winds.
If the storm reaches the higher estimate of $20 billion in damage, that would put it ahead of Hurricane Irene, which raked the Northeast in August 2011 and caused $16 billion in damage. Hurricane Katrina, which killed 1,200 people, cost $108 billion.
The Associated Press contributed to this report.