US President Barack Obama toured New Jersey’s devastated coastline on Wednesday, vowing to stay with flood victims "for the long haul" as the US toll from superstorm Sandy passed 70.

US President Barack Obama toured New Jersey's devastated coastline on Wednesday, 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. 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.

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.