New Yorkers on high alert as Hurricane Irene storms on

Some 65 million people along America’s east coast were braced last night for a hurricane that could inflict billions of dollars in damages in an arc from Washington to Baltimore, Philadelphia, New York and Boston.

Rain borne by Hurricane Irene’s outer bands was already reaching the southeast of North Carolina, but the main thrust of the hurricane was not expected in North Carolina until today.

President Barack Obama last night warned Irene was likely to be “an extremely dangerous and costly storm”. It would be the strongest to strike the eastern seaboard in seven years.

Irene weakened slightly yesterday, dropping to a category two storm with maximum winds of 110mph. But she could regain strength and is expected to be between a category two or three when she hits North Carolina, the US National Hurricane Centre said.

The hurricane destroyed hundreds of homes on small Bahamian islands but largely spared the capital of Nassau as it tore through the archipelago on Thursday. Some small settlements reported up to 90 per cent of homes were damaged.

The US warning area was expanded to cover the coast from North Carolina north to Sandy Hook, New Jersey, which is just south of New York City.

A hurricane watch extended even further north and included Long Island, and the islands of Martha’s Vineyard and Nantucket in Massachusetts.

North Carolina was just first in line along the eastern seaboard – home to some of America’s most heavily populated areas and some of its most valuable real estate.

Major cities, suburbs, ports, airports, road networks, farmland and mile after mile of beachfront neighbourhoods are also in harm’s way.

Max Mayfield, the National Hurricane Centre’s retired director, said: “One of my greatest nightmares was having a major hurricane go up the whole north-east coast. This is going to be a real challenge … There’s going to be millions of people affected.”

Hundreds of thousands of New Yorkers have been told to prepare to leave. The city has not seen a hurricane in decades.

The Federal Emergency Management Agency (Fema) was yesterday preparing for the worst.

Fema director Craig Fugate said: “We’re going to have damages, we just don’t know how bad. This is one of the largest populations that will be impacted by one storm at one time.”

Latest forecasts had Irene crashing up the North Carolina coastline today, then churning up from Virginia to New York City before a much-weakened storm reaches New England.

Even if the winds are not strong enough to damage buildings in New York, much of its subway system and other infrastructure is underground and subject to flooding. The city’s two main airports are also close to water and could be inundated, as could densely populated low-lying neighbourhoods.

Irene could cause billions of dollars in damages in a worst case scenario, said Kathleen Tierney, director of the Natural Hazards Centre at the University of Colorado.

In the past 200 years, New York has seen only a few significant hurricanes. In September 1821, a hurricane raised tides by 13ft in an hour and flooded all of Manhattan south of Canal Street, the area which now includes Wall Street.

New England is also unaccustomed to direct hits from hurricanes. Hurricane Gloria was the last to strike in 1985.

The first US injuries from Irene appeared to be in South Florida near West Palm Beach where eight people were washed off a jetty on Thursday by a large wave.