Tens of millions of people were hunkered down Monday, bracing for howling winds, torrential downpours and storm surges that authorities warned could bring devastation unlike anything they've seen.
Hurricane Sandy could affect as many as 60 million people.
"This is the most catastrophic event that we have faced and been able to plan for in any of our lifetimes," Connecticut Gov. Dan Malloy said.
An expected storm surge at midnight could raise water levels to 11 feet above normal high tide, bringing "the potential to cause unprecedented damage."
Two dozen people in Delaware who had ignored mandatory evacuations were taken to shelters overnight. Gov. Jack Markell, on Twitter, said they were "rescued from flooding," but the state government later told CNN that they were not emergency rescues.
Officials across the Eastern Seaboard had implored residents over the weekend to evacuate, emphasizing that authorities could be endangered if they tried to save them. New Jersey Gov. Chris Christie put it bluntly: "Don't be stupid. Get out!"
Hundreds of thousands of people have abandoned their homes. New York City landmarks are eerily empty. The nation's capital is emptied of government workers. Much of the region was settling into paralysis, bracing for what's to come.
From North Carolina to Maine, forecasters said Sandy was likely to collide with a cold front and spawn a "superstorm" that could generate flash floods, snowstorms and massive power outages.
The National Grid, which provides power to millions of customers, said 60 million people could be affected -- up from its previous estimate of 50 million.
"It could be bad," said U.S. Coast Guard Rear Adm. Steven Rattior, "or it could be devastation."
The impact goes beyond the East Coast. Wave heights in Lake Michigan could reach 28 feet Monday night and 31 feet by Tuesday, the National Weather Service said.
Eight days before Election Day, President Obama and his challenger Mitt Romney have canceled or changed planned campaign events because of the storm.
Obama returned Monday from a canceled campaign event in Orlando to Washington, where he went directly into a briefing, the White House said. He was to deliver a statement on Sandy at 12:45 p.m.
Sandy has already claimed at least 67 lives -- 51 in Haiti -- on its path last week across the Caribbean.
In the United States, federal, state and local officials have been working to convince those in vulnerable areas that Sandy is dangerous.
"My biggest concern is just people not taking it seriously and not taking the proper precautions," Newark Mayor Cory Booker told CNN early Monday. "We still have some time for people to get ready. ... We anticipate there could be many days without power afterward."
On Monday, Sandy started to turn toward the United States, putting it on course for landfall late Monday or early Tuesday.
At 11 a.m., the Category 1 hurricane was 205 miles southeast of Atlantic City, New Jersey, and 260 miles south-southeast of New York City, the National Hurricane Center said. Maximum sustained winds were 90 mph, and Sandy was moving north-northwest at 18 mph.
Hurricane-force winds extended outward 175 miles from the storm's center, and tropical storm-force winds reached 485 miles.
It was predicted to turn toward the northwest soon, and turn toward the west-northwest Monday night. Its center was expected to make landfall along or just south of the coast of New Jersey on Monday evening or Monday night.
Gale-force winds were already occurring over parts of the Mid-Atlantic states -- from North Carolina up to New York's Long Island. The winds were expected to spread later in the day over more of the Mid-Atlantic coast, New York City and southern New England.
Storm surge -- the combination of a storm and a high tide -- "will cause normally dry areas near the coast to be flooded," the weather service said. It said water depths could reach 6 to 11 feet along Long Island Sound and New York Harbor.
"Elevated waters could occur far removed from the center of Sandy," it added.
Three to 6 inches of rain were expected over far northeastern North Carolina, with isolated maximum totals of 8 inches possible, it said.
Four to eight inches of rain were expected over portions of the Mid-Atlantic states, with isolated amounts of 12 inches possible.
Two to 3 feet of snow were expected to accumulate in the mountains of West Virginia and 1 to 2 feet in the mountains of southwestern Virginia to the border with Kentucky. One to one-and-a-half feet of snow were expected in the mountains near the North Carolina-Tennessee border.
But even with Sandy hundreds of miles offshore, officials were warning of its life-threatening storm surge flooding portions of the Mid-Atlantic, including low-lying areas of New York and New Jersey.
Michelle Franchaise of Ocean Gate was among the tens of thousands of New Jersey residents ordered to leave their