Post-tropical cyclone Sandy, one of the biggest storms ever to hit the United States, has roared ashore with fierce winds and heavy rain near the resort of Atlantic City, New Jersey.

Having forced evacuations, shut down transportation and interrupted the presidential campaign, high winds and flooding racked hundreds of miles of Atlantic coastline, while heavy snows were forecast farther inland as the centre of the storm marched westward.

The ferocious storm has been blamed for ten deaths across several states.

More than three million customers were left without power by early on Monday evening, while many communities were swamped by flood waters.

Television images showed water rising to historic heights in lower Manhattan, raising the possibility of flooding in the city's subway system.

"In the olden days, you would have had lots of fatalities. We're not through this yet. ... It may be as bad of a storm as we've ever seen, but I would expect the damage to be relatively minor," New York City Mayor Michael Bloomberg told a Monday evening news conference.

Elsewhere on the east side of Manhattan, nineteen workers were reported as being trapped inside a power station by rising floodwaters. A rescue worker, who declined to be named, said the station had suffered an explosion inside.