New York City moved closer to resuming its frenetic pace by partially getting back its vital subways Thursday, three days after Superstorm Sandy, but neighbouring New Jersey was stunned by coastal devastation and the news of thousands of people in one city still stranded by increasingly fetid flood waters.

The decision to reopen undamaged parts of the United States' largest transit system came as the death toll reached more than 90 in the U.S. — 39 in New York City alone — and left more than 4.6 million homes and businesses without power. Hurricane Sandy earlier left another at least 69 people dead as it swept through the Caribbean.

Passengers exit a downtown-bound subway train in New York's Times Square on Thursday. (Richard Drew/Associated Press)

The total damage in the U.S. from Superstorm Sandy could run as high as $50 billion US, according to the forecasting firm Eqecat. That would make it the second-costliest storm in U.S. history after Hurricane Katrina. The estimate includes property damage and lost business.

In New York, people streamed into the city as service began to resume on commuter trains and subways. The three major airports resumed at least limited service, and the New York Stock Exchange was open again. Amtrak's northeast corridor — the busiest train line in the country — was to take commuters along the heavily populated East Coast again starting Friday.

But hundreds of people lined up for buses, traffic jammed for kilometres and long gas lined formed. And the latest deaths reported included two young boys who disappeared Monday night when waves of water crashed into an SUV.

Hundreds of thousands in New York City alone were still without power, especially in downtown Manhattan, which remained in the dark roughly south of the Empire State Building after floodwaters had knocked out electricity. Con Edison said it was on track to restore power by Saturday.

Concerns rose over the elderly and poor all but trapped on upper floors of housing complexes in the powerless area and facing pitch-black hallways, elevators and dwindling food. New York's governor ordered deliveries of food and drinking water to help them. New York dipped to about 4 C Wednesday night.

"Our problem is making sure they know that food is available," New York City Mayor Michael Bloomberg said Thursday, as officials expressed concern about people having to haul water from fire hydrants up darkened flights of stairs.

'Everyone's leaving'

In Manhattan's Chelsea neighbourhood, Mary Wilson, 75, walked downstairs from her 19th floor apartment for the first time Thursday because she ran out of bottled water and felt she was going to faint. She said she met people on the stairs who helped her down.

"I did a lot of praying: 'Help me to get to the main floor.' Now I've got to pray to get to the top," she said, buying water from a convenience store. "I said, 'I'll go down today or they'll find me dead."'

In another neighbourhood, Rima Finzi-Strauss was fleeing her apartment and taking a bus to Washington.

"We had three guys sitting out in the lobby last night with candlelight, and very threatening folks were passing by in the pitch black," she said. "And everyone's leaving. That makes it worse."

In New Jersey, the once-pristine Atlantic coastline famous for Bruce Springsteen and the TV show Jersey Shore was shattered. President Barack Obama joined Gov. Chris Christie in a helicopter tour of the devastation Wednesday and told evacuees, "We are here for you. We are not going to tolerate red tape. We are not going to tolerate bureaucracy."

A man looks over the debris on the Seaside Heights, N.J., beach near Casino Pier on Wednesday. (David Gard/Star-Ledger/Associated Press)

Some residents finally got a look at what was left of their homes. Sandy wrecked houses, businesses and boardwalks.

"A lot of tears are being shed today," said Dennis Cucci, whose home near the ocean in Point Pleasant Beach was heavily damaged. "It's absolutely mind-boggling."

And warnings rose again about global warming and the prospect of more such severe weather to come.

"The next 50 to 100 years are going to be very different than what we've seen in the past 50 years," said S. Jeffress Williams, a scientist emeritus at the U.S. Geological Survey's Woods Hole Science Center in Massachusetts. The sea level is rising fast, and destructive storms are occurring more frequently, said Williams, who expects things to get even worse.

Across the Hudson River from New York City, the floodwaters were slowly receding in the city of Hoboken, where an estimated 20,000 people had remained in their homes. The National Guard was helping with evacuations, but residents were warned not to walk around in water that was tainted with sewage and chemicals from the heavily industrial region.

Fights break out

New Jersey residents across the state were urged to conserve water. At least 1.7 million customers remained without electricity there, and fights broke out as people waited in long lines for gas.

The superstorm's effects, though much weakened, continued Thursday. Snow drifts as high as 1.5 metres piled up in West Virginia, where the former hurricane merged with two winter weather systems as it went inland.

Across the region, people stricken by the storm pulled together, in some cases providing comfort to those left homeless, in others offering hot showers and electrical outlets for charging mobile phones to those without power.

Bloomberg also ordered residents to share cars. Television footage Thursday showed heavy traffic crawling into Manhattan as police turned away cars that carried fewer than three people — a rule meant to ease the congestion that paralyzed the city earlier in the week.

But frustration mounted and tempers flared in gas lines.

At a station near Brooklyn's Coney Island, almost 100 cars lined up, and people shouted and honked, and a station employee said he had been spit on and had coffee thrown at him.

At a Brooklyn arena, more than 1,000 people packed the sidewalk waiting for buses to Manhattan. When a bus pulled up, passengers rushed the door. A transit worker banged on a bus window, yelled at people inside, and then yelled at people in the line.

After suffering the worst disaster in its 108-year-old history, the subways were rolling again — at least some of them. More than a dozen of the lines would offer some service, but none below Manhattan's 34th Street.

But most of New Jersey's mass transit systems remained shut, leaving hundreds of thousands of commuters stuck on clogged highways and in long lines at gas stations. Atlantic City's casinos remained closed.

Signs of the good life that had defined wealthy New Jersey shorefront enclaves lay scattered and broken: $3,000 barbecue grills buried beneath the sand and hot tubs cracked and filled with seawater. Nearly all the homes were seriously damaged, and many had disappeared.