Hurricane Irene has made landfall on the US east coast, bringing winds of more than 85 mph (140km/h), as it hit North Carolina. More than two million people have been ordered to leave their homes ahead of the massive category one storm. In New York city, a quarter of a million people living in low-lying areas have been told to leave in an unprecedented mandatory evacuation. The city mayor warned it was "foolish" and "dangerous" to ignore the order. Irene is a "life-threatening storm" for New Yorkers, Michael Bloomberg told a news conference early on Saturday. New York State is one of seven states from North Carolina to Connecticut have declared emergencies. 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. All of us have to take this storm seriously," he said on Friday, before cutting short his holiday in Martha's Vineyard on the Massachusetts coast, 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 expects Irene to weaken in strength after hitting North Carolina, but it is forecast to remain a hurricane as it moves north along the mid-Atlantic coast on Sunday. 'Dangerous surges' The eye of the storm crossed the North Carolina coast near Cape Lookout at about 0730 local (1130 GMT) on Saturday. "Extremely dangerous" storm surges have been forecast in parts of the state that could raise water levels by as much as 11ft (3.35m). About 200,000 residents, mostly in the southern coastal area of North Carolina, were without power on Saturday morning as a result of Irene, a power company spokeswoman told Reuters news agency. More than 200,000 people had already evacuated coastal areas 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. Further north, tens of thousands of people are on the move in parts of Delaware, Maryland, New Jersey and New York City after mandatory evacuations were ordered for people living in low-lying areas. In New York city, parts of Manhattan and into Staten Island are at particular risk, according to projections issued by city authorities. The city's transport systems, including the subways and airports, are to shut from 1200 local on Saturday (1600 GMT). Hospitals in affected areas of the city have begun evacuating patients. In Washington DC, Sunday's dedication of the new memorial for Martin Luther King Jr - which President Obama had been expected to attend - has been postponed until at least September. The power company serving the Washington area warned of "potential widespread power outages" at the weekend. Amtrak, the US rail network, announced it was cancelling services between Washington and Boston from Saturday, having already suspended operations south to Virginia and beyond. Supermarkets along the east coast are reportedly running out of supplies as people stock up before the storm arrives. "Earlier I was in the supermarket and it was absolute chaos - no shopping carts available, torch batteries sold out, everyone buying up bottled water and that kind of thing," Oliver Brew of Brooklyn in New York told the BBC. Alex Schlesinger of Virginia Beach in Virginia, which neighbours North Carolina, said stores were also busy there and petrol stations were running dry. The Pentagon has loaded 200 trucks with emergency supplies, and 100,000 National Guard troops are on standby. The American Red Cross said it was preparing dozens of emergency shelters along the east coast. The north-eastern seaboard is the most densely populated corridor in the US, with more than 65 million people living in major cities along the coast from Washington DC in the south to Baltimore, Philadelphia, New York and Boston further north. States of emergency have been declared in North Carolina, Maryland, Virginia, Delaware, New Jersey, New York and Connecticut. "We're going to have damages, we just don't know how bad," Craig Fugate, head of the US Federal Emergency Management Agency, told the Associated Press news agency. "This is one of the largest populations that will be impacted by one storm at one time." If Irene hits New York and New England at category two, it will be the region's strongest storm since Hurricane Bob glanced off Massachusetts in 1991, and Hurricane Gloria, which caused extensive damage to New York City in 1985.