Hurricane Sandy could affect as many as 60 million people.
An expected storm surge at midnight could raise water levels to 11 feet above normal high tide, bringing "the potential to cause unprecedented damage."
As of Monday afternoon, 116,000 customers were without power in seven states.
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.
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 from North Carolina to Maine.
The National Grid, which provides power to millions of customers, said 60 million people could be affected.
"It could be bad," said U.S. Coast Guard Rear Adm. Steven Rattior, "or it could be devastation."
The predicted impact extends 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 with both candidates locked in a tight race, President Barack Obama and his Republican challenger Mitt Romney canceled or changed planned campaign events because of the storm.
Obama returned to Washington on Monday from Florida and went directly to a White House Situation Room briefing on the storm. He then told reporters that he was confident that assets had been positioned for an effective response to the aftermath of the storm.
He, too, urged those in the path of the storm to heed warnings and other instructions.
"The most important message I have for the public right now is please listen to what your state and local officials are saying," Obama said. "When they tell you to evacuate, you need to evacuate."
In Avon Lake, Ohio, Romney asked supporters to drop off items and cash at his "victory centers" to be donated to victims of the storm.
"There are families in harm's way that will be hurt -- either in their possessions or perhaps in something more severe," Romney said.
The campaign canceled events that had been planned for later in the day and Tuesday for Romney and his running mate, Rep. Paul Ryan.
Sandy claimed at least 67 lives -- 51 in Haiti -- on its path last week across the Caribbean.