An intensified Hurricane Sandy is roaring up the US East Coast, threatening major floods and power cuts that could affect 60 million people.

Hundreds of thousands of residents have been ordered to evacuate New York City and New Jersey.

Public transport has been suspended in cities up the eastern seaboard and thousands of flights grounded.

Forecasters fear Sandy will become a super-storm when it collides with cold weather fronts from the west and north.

The category one hurricane has already killed 69 people – 52 of them in Haiti – after sweeping through the Caribbean in the past week.

Slow-moving storm

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At the White House, President Barack Obama warned Americans in harm’s way to follow emergency instructions.

“When they tell you to evacuate, you need to evacuate,” said Mr Obama, who has cancelled campaign events eight days before the US elections.

“Do not delay. Don’t pause. Don’t question the instructions that are being given, because this is a serious storm and it could potentially have fatal consequences.”

The president has signed nine emergency declarations covering New York, New Jersey, Massachusetts, Connecticut, Rhode Island, Delaware, Pennsylvania, Maryland and District of Columbia.

The storm threatens an 800-mile (1,290-km) swathe of the US, from the Atlantic Ocean to the Great Lakes in the Mid-West.

Up to 3ft (91cm) of snow is expected to fall on the Appalachian mountains in West Virginia, Virginia and Kentucky.

At 17:00 EDT (21:00 GMT), Sandy was churning about 30 miles south-east of Cape May, New Jersey, the National Hurricane Center (NHC) said.

The hurricane strengthened on Monday, packing maximum sustained winds of 90mph with higher gusts.

Hurricane force winds extended for 175 miles and tropical storm force winds for 485 miles, the NHC added.

Authorities said that high tides swelled by a full moon could create storm surges of up to 11ft.

The eye of the weather system, which has been dubbed Frankenstorm, is expected to make landfall just south of the New Jersey coast on Monday evening, the NHC said.

Forecasters say Sandy could linger over as many as 12 states for 24-36 hours.

President Obama cancelled a planned rally in Florida with former President Bill Clinton on Monday and an event for Tuesday in Wisconsin, far from the storm.

His Republican challenger, Mitt Romney, held two rallies as planned in the Mid-West, but cancelled events later on Monday and Tuesday.

Amtrak has halted passenger train services across the north-east, while almost 9,000 flights were cancelled, according to Flightaware.com.

With public transport suspended in New York, Washington DC, Baltimore, Philadelphia and Boston, many workers stayed at home on Monday.

Authorities closed the Holland Tunnel under the Hudson River between New York and New Jersey. Maritime operations at shipping terminals in that region were also suspended.

As many as 300,000 customers in seven states are without power, CNN reported.

The Hudson and East rivers in New York City have begun overflowing their banks.

Officials warned that flooding in lower Manhattan could inundate the city’s underground electric and communications lines and subway system.

Trading on the New York Stock Exchange and Nasdaq were suspended on Monday and will be shut on Tuesday as well. The United Nations headquarters in New York has also been closed.

In Manhattan, a giant construction crane has partially collapsed and is dangling atop a 65-storey skyscraper. No injuries were reported.

Mass evacuations are under way in low-lying coastal areas from Maryland to Connecticut.

Some 375,000 residents were ordered out of lower Manhattan and other areas of New York. The city has set up shelters for the displaced in scores of schools.

Another 50,000 residents were ordered to leave their homes in Delaware.

Some 30,000 were ordered to evacuate Atlantic City, New Jersey, much of which was underwater.

Chincoteague Island on the Virginia coast was reported to be entirely submerged under water.

In Ocean City, Maryland, a tourist pier was severely damaged.

The Pentagon has activated 1,500 members of the National Guard and made available 140 helicopters for rescue and relief efforts.

At least 14 out of 16 people on board a replica of HMS Bounty – built for the 1962 film Mutiny on the Bounty – had to be rescued earlier off North Carolina after the ship began taking on water.

Two crew members did not make it to life rafts and remain missing

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