Packing a powerful punch, Hurricane Sandy slammed into New Jersey Coast plunging more than three million into darkness and crippling transportation across the US East Coast.

Though downgraded to a "post-tropical" superstorm Monday evening by the National Hurricane Centre, Sandy still unleashed powerful winds and torrential rains from North Carolina to Maine and knocked out power to nearly three million customers across 11 states and the national capital.

Subways and bridges were shut down and streets were quiet as gusts howled over a huge region encompassing hundreds of miles, CNN reported.

The storm hit land near Atlantic City about 8 p.m. (6:30 a.m. India time Tuesday) packing 80-mph winds at landfall, down from the 90 mph clocked earlier Monday.

Hurricane-force winds stretched from Cape Cod to the Virginia coast as Sandy swept ashore, with its storm surge setting new high-water records for lower Manhattan and swamping beachfronts on both sides of Long Island Sound.

Mass transit shut down across the densely populated Northeast, landmarks stood empty and schools and government offices were closed. The National Grid, which provides power to millions of customers, said 60 million people could be affected before it's over.

In New York, lower Manhattan's Battery Park recorded a 12.75-foot tide, breaking a record set in 1960 with Hurricane Donna. The city halted service on its bus and train lines, closing schools and ordering about 400,000 people out of their homes in low-lying areas of Manhattan and elsewhere.

As New York's skyscrapers were being battered with higher winds a crane snapped and dangled from the side of a luxury high-rise under construction Far above West 57th Street. Police closed part of the street and evacuated several nearby buildings, including the Parker Meridien hotel.

By Monday afternoon, 23 states were under a warning or advisory for wind related to Sandy. Thousands of flights had been cancelled, and hundreds of roads and highways were expected to flood..

Winter storm warnings were issued through Wednesday morning for southwest Virginia and the East Tennessee mountains, where snow had already started falling, according to NBC News.

More than 30 inches of snow was expected in the higher elevations of West Virginia, and a foot was forecast in the North Carolina mountains.

With the storm expected to linger longer than most, the federal workforce and public employees in the national capital, Maryland and Virginia were told to stay home for a second day on Tuesday.

Local schools in Wasgungton and adjoining states were shut down. Metro and other transit agencies planned to remain out of service Tuesday.

No flights were expected Tuesday in or out of the region's three airports, where scores of travellers were stranded Monday after airlines halted service throughout the Northeast.