President Barack Obama toured New Jersey's devastated coastline, vowing to stay with flood victims "for the long haul" as the US toll from superstorm Sandy passed 70.
In New York, the stock exchanges and John F. Kennedy and Newark Liberty airports reopened on Wednesday. But more than six million homes and businesses, the majority of them in New York state and neighboring New Jersey, remained without power.
The full extent of one of the largest and most destructive storms ever to strike the United States became clearer, with entire coastal communities in Maryland, Delaware and New Jersey submerged or cut off by floodwaters.
US media reports said 72 Americans had been confirmed dead across 15 storm-ravaged states, bringing Sandy's overall toll to 144, including Canada and the Caribbean, where Haiti and Cuba were hit particularly hard.
Just six days before Americans vote on whether he should have a second four-year term, Obama surveyed the damage in New Jersey, where a massive relief operation had swung into gear with tens of thousands of homes under water.
Taking a third day off the campaign trail to manage the response to the disaster despite Tuesday's looming election, Obama, accompanied by New Jersey Governor Chris Christie, offered a show of strength and support to victims.
"You guys are in my thoughts and prayers. We are going to be here for the long haul," he told a group of evacuees at a makeshift shelter.
Obama and Christie clambered aboard the president's Marine One helicopter to fly over New Jersey's Atlantic coast -- over houses tipped off their foundations, streets inundated with sand, and still-flooded neighborhoods.
In the community of Seaside Heights, Obama saw the twisted iron of a storm-battered amusement park and a nearby pier that was ripped apart.
Although the main focus was on New Jersey and New York, particularly lower Manhattan and Long Island, Obama said he was also concerned about Connecticut and West Virginia, where heavy snows had made certain areas inaccessible.
"We are here for you. And we will not forget. We will follow up to make sure that you get all the help that you need until you've rebuilt," he said.
While many towns and cities along the US East Coast remained paralyzed following Monday's onslaught by superstorm Sandy, buses were back on New York streets and Governor Andrew Cuomo announced that limited subway services would resume Thursday, with free fares through Friday.
"The gridlock we experienced yesterday shows that the New York metropolitan region is in a transportation emergency," Cuomo said in a statement, expressing hope that the free ride would encourage commuters to leave their cars at home.
Limited commuter rail service to New York suburbs has also resumed, while Mayor Michael Bloomberg announced temporary car pooling rules to reduce the gridlock choking Manhattan.
New York's LaGuardia airport was also expected to reopen on Thursday. At last count, 19,500 flights had been cancelled because of Sandy, tracking service flightaware.com said.
The UN Security Council also reopened, after suffering flooding from the East River.
Despite these improvements, large sections of New York, including many skyscrapers in lower Manhattan, remained without electricity, and schools throughout the city were to remain shuttered for the rest of the week.
Bellevue Hospital, the oldest in the country, decided to evacuate its remaining 500 patients on Wednesday after flooding inundated the basement and knocked out electricity.
In nearby Hoboken, on the New Jersey side of the Hudson River, people in flooded homes were still waiting for rescue, while in Jersey City, a night curfew was declared in the wake of looting.
Meanwhile, some 300,000 gallons of diesel spilled into the waters off New York City when a storage tank at a nearby New Jersey refinery ruptured, prompting a massive containment and clean-up effort, CNN reported.
The presidential election campaign, which went into a hiatus during the storm, stirred back to life in the final run-up to election day on November 6.
Romney gingerly returned to the campaign trail in the key swing state of Florida, but he too addressed the plight of storm-battered Americans hundreds of miles to the north.
"If you have an extra dollar or two, please, send them along and keep the people who have been in harm's way... in your thoughts and prayers," he told about 2,000 people in an airport hangar in Tampa.
Some 10,000 National Guard troops have deployed to storm-hit states to help local authorities rescue stranded survivors, remove debris, direct traffic and assess the damage from the air, the Pentagon said.
Army engineers stood ready to provide pumps and generators as needed while the US Navy sent out three amphibious ships off the New Jersey coast in case state governments requested aid for rescue operations.
Insured losses from Sandy could run between seven and 15 billion dollars (5.4 to 11.5 billion euros), according to initial industry estimates.