MILLIONS of people are without power amid record-breaking storm surges as one of the biggest storms ever to hit the United States reaches the East Coast.

Forecasters in the US have downgraded Sandy from a hurricane to a post-tropical storm, but said it is still a dangerous system that is heading straight for New Jersey and Delaware.

Although the storm is losing strength as it makes landfall, it has sustained winds of 85mph.

The US National Hurricane Centre in Miami said the centre of the enormous storm made landfall at 8pm local time near Atlantic City.

It hurled a record-breaking 13ft surge of seawater at New York City on Monday, after washing away part of the Atlantic City boardwalk.

In an attempt to lessen damage from the storm, New York City's main utility firm cut power to about 6,500 customers in lower Manhattan.

Authorities are worried that seawater will seep into the New York subway and cripple it, along with the electrical and communications systems that are vital to the nation's financial centre.

The storm has already knocked out electricity to more than 1.5 million people.

The normally bustling streets of New York were left eerily deserted as the city awaited the arrival of the storm.

The freak weather – dubbed a “Frankenstorm” by the US media – forced the closure of the Wall Street Stock Exchange for the first time since 9/11. The stock exchange will remain closed on Tuesday.

The subway has been halted and hundreds of thousands of people evacuated from low lying areas.

In the UK all flights to the Eastern seaboard of the United States were cancelled.

The weather front is expected to wreak havoc along an 800-mile wide front from the East Coast to the Great Lakes. Behind it freezing winds are predicted to lay down up to 3-ft of snow in some areas.

Airports closed, and authorities warned that the time for evacuation was running out or already gone. Many workers planned to stay home as subways, buses and trains shut down across the region under the threat of flooding that could inundate tracks and tunnels. Widespread power failures were anticipated.

President Barack Obama cut short his campaigning for the Presidential election to declare a state of emergency in Massachusetts, Connecticut, Rhode Island, New York, New Jersey and Pennsylvania, authorising federal relief work to begin well ahead of time. He promised the government would ‘‘respond big and respond fast’’ after the storm hits.

Authorities warned that New York could get hit with a surge of seawater that could swamp parts of lower Manhattan, flood subway tunnels and cripple the network of electrical and communications lines that are vital to the nation’s financial centre.

‘‘If you don’t evacuate, you are not only endangering your life, you are also endangering the lives of the first responders who are going in to rescue you,’’ mayor Michael Bloomberg warned.

‘‘This is a serious and dangerous storm.’’

The storm has already claimed 65 lives as it tore through the Caribbean.

Earlier a replica sailing ship sank after its crew was forced to abandon it off the coast of Cape Hatteras, North Carolina.

The ship, a replica of HMS Bounty, was used in the Pirates of the Caribbean movies.

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