Markets and airports reopened in New York and New Jersey on Wednesday, with President Barack Obama due to arrive in the region to see the worst of the damage for himself.
The so-called superstorm, which began as Hurricane Sandy, was responsible for at least 50 deaths, authorities in five US states said, but New Jersey took the brunt of its impact on Monday night and faces the biggest challenge in rebuilding.
Political analysts said Mr Obama would reap considerable advantage in the presidential race from the television coverage of his arrival and tour of the state, where he will be shown the extent of devastation by its Republican governor, Chris Christie. Both Mr Obama and his Republican challenger Mitt Romney halted their campaigns on Monday and Tuesday.
Mr Christie, who has been a trenchant critic of the president, was full of praise for him on Tuesday as Mr Obama declared New Jersey and its neighbour New York to be significant disaster sites, and on Wednesday extended the area to include Connecticut, entitling them to immediate federal relief.
After his tour of the disaster zone, Mr Obama plans to return to the campaign trail on Thursday with a trip to the swing states of Colorado and Nevada.
The clean-up of Manhattan was under way, but beyond the human cost of 22 dead in the city, the damage caused by a record storm surge of 14ft has left tunnels and subway stations inundated, power generators ruined and cars and property irreparably afflicted.
Mayor Michael Bloomberg rang the opening bell of the New York Stock Exchange in a symbolic moment of the city reopening for business.
Across the northeastern states most affected, an estimated 8.2m people were still without power on Wednesday. Mr Christie said that in his state, which suffered six fatalities in the storm, it could take a week to 10 days to restore all homes to the power grid.
The clean-up of the New York subway system is also expected to take several days, while bus services were running at almost full strength.
John F. Kennedy and Newark airports were operating some flights, but La Guardia remained flooded and closed. The storm has caused 19,000 flight cancellations.
Residents of downtown Manhattan were worst affected. Buildings remained powerless, restaurants and businesses stayed closed, traffic lights were still broken and mobile phone service was patchy at best.
In a sharp contrast, the storm barely interrupted the routines of those living further uptown. Time Square's advertising billboards gleamed, lines formed outside midtown coffee shops and joggers, dogwalkers and mothers with prams returned to their daily regimes.
Those preparing for the New York marathon, the 26.2 mile race through Brooklyn, Queens and into Manhattan scheduled to be held on Sunday, continued their training along Central Park.
In the Hell's Kitchen and Upper West Side neighbourhoods on Manhattan's west side, most shops and restaurants were open, with crowds at pubs spilling on to the sidewalks on Tuesday night and queues forming at grocery stores.
Downtown residents trekked north in search of power points, mobile phone signal and internet connection. People hovered around daisy chains of power strips plugged into the walls shops and restaurants, hoping to charge their phones while others lined up to use payphones.
At a Hertz car rental office, dozens of people with luggage queued in hopes of getting a vehicle that could take them out of the city. Others chose to walk, drive, cycle or even rollerblade or skateboard to their destinations.
But just like the Grinch stole Christmas, Sandy stole Halloween. New York City's annual costumed parade through Manhattan's Greenwich Village has had to be postponed and trick or treaters have had to find alternate routes as many streets remains cordoned off due to building and street damage.
View from downtown
In the darkened lobby of the Gem Hotel on West 22nd Street, the receptionist said she had been driven to work by a friend on Wednesday morning and had seen no sign of the bus services due to restart the previous day.
As the silhouettes of colleagues with head lamps on their foreheads stalked around, Sean Ames, the hotel's general manager, said staff and guests were doing fine in the circumstances.
"The first day (without power) is tough, but once you get beyond that it becomes routine," he said. "The resilience of people is amazing."
Some guests stranded by airport closures had moved to hotels with power, but most had stayed. With the elevators disabled they were using the stairs of the six storey building, and were getting supplies of coffee and snacks from staff on foraging missions to illuminated streets a few blocks north.
Mr Ames said he was prepared to be without power for days. "We have charged the [back-up battery] so guests can plug in their phones - and as long as they have their phones the world isn't so bad."
Standing unhappily in the cold outside the Chelsea International Hostel was Laurie Girard, a French student from Poitiers who had come to New York with a group of friends on an English study trip.
She summarised life in the hostel as: "No hot water. No light. Rotten."
Asked what they were eating, she and her friends dug their hands into their pockets and pulled out apples. "Pomme," she said glumly. They did not know where their next meal was coming from.
In spite of the cold water they had forced themselves to shower, said Debora Tenot, another French student. "We have to. We can't live like pigs."
On Wednesday they planned to visit the Empire State Building, which is in a zone with power, though not with any great enthusiasm.
Their flight home on Saturday seemed a long way away, but other hotels they'd looked at moving to were either full or too expensive . "We've got to stay here. We have no choice," said Ms Girard.
Additional reporting by Anjli Raval, Johanna Kassel, Barney Jopson, David Gelles, Christopher Booker, Emily Steel, Elizabeth Paton in New York.