Millions in US urged to flee path of Hurricane Irene

The mayor of New York has ordered an unprecedented evacuation of a quarter of a million people living in low-lying parts of the city.

Seven states from North Carolina to Connecticut have declared emergencies ahead of Irene's arrival.

US President Barack Obama has warned Irene could be "a historic hurricane".

He has urged people in the projected path of Hurricane Irene - the first hurricane of the Atlantic season - to take precautions.

"Don't wait, don't delay. We all hope for the best, but we have to be prepared for the worst. All of us have to take this storm seriously," he said on Friday, before cutting short his holiday in Martha's Vineyard, an island on the Massachusetts coast, a day early to head back to Washington.

The National Hurricane Center has downgraded Irene from a category two to a category one hurricane but says it is still packing hurricane-force winds of 90mph (150km/h) that extend outwards some 90 miles (150km). Tropical-force winds extend as far as 290m (465km).

The NHC says Irene is expected to weaken in strength after it hits the coast of North Carolina later on Saturday morning, but is forecast to remain a hurricane as it moves north along the mid-Atlantic coast on Sunday.

More than 200,000 people have already evacuated coastal parts of North Carolina as high waves and strong winds began to lash islands just off the mainland. Residents hoping to ride out the storm have stocked up on food, water and fuel.

Forecasters have warned of "extremely dangerous" storm surges in parts of North Carolina that could raise water levels by as much as 11 ft (3.35m).

"Stores are busy, petrol stations are running dry but thankfully I prepared myself last night with supplies," said Alex Schlesinger of Virginia Beach in the neighbouring state of Virginia, also in the hurricane's path.

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