Millions across eastern seaboard left without power and at risk of flooding despite hurricane being downgraded to tropical storm New York breathed a sigh of relief on Sunday after hurricane Irene caused far less damage in the city than feared, but the storm still caused deaths, serious floods and power blackouts affecting more than a million people as it swept up the north-eastern seaboard of the United States. Irene weakened quickly after making landfall near Atlantic City, New Jersey, at about 5.30am local time. By the time it made landfall again, at Coney Island four hours later, Irene had been downgraded by the National Hurricane Center to a tropical storm with winds at around 65mph – much weaker than the 85mph that was forecast late on Saturday. But while the storm failed to bring the devastating surge that had been feared in New York, it was still powerful enough to cause three deaths and widespread damage in outer suburbs and neighbouring states. In New Jersey a 20-year-old woman was found dead in her car on a flooded rural road. The woman, who has not yet been identified, had earlier called police after she and her car were washed away by a flash flood. “She left her house, went in her car and was swept away,” said New Jersey governor Chris Christie. About 30 miles (48km) north-west of Manhattan in New York’s Rockland County, a man was electrocuted by a downed power line after he tried to save a child who had gone out into a flooded street that had live wires, officials said. The child is now in hospital in a serious condition. And in Prospect, Connecticut another person was killed in a fire that investigators believe was sparked by fallen wires. After passing New York the storm continued north, causing extensive flooding in upstate New York, Connecticut and New England. President Barack Obama warned the storm and its aftermath were not over: “This is a storm that has claimed lives. Our thoughts and prayers are with those who have lost loved ones,” he said. “Many Americans are still at serious risk of power outages and flooding which could get worse in the coming days. I want people to understand that this is not over.” The death toll now stands at more than 15 with lives lost all along the storm’s track from the Carolinas to Virginia and up through Pennsylvania, where a man was killed in his tent by a falling tree, to New York and beyond. A nuclear reactor in Maryland was shut down after it was damaged by wind. Others were taken offline or were operating at reduced capacity as precautionary measures. More than six million homes and businesses lost power as the storm passed up the east coast. Two million people were warned or ordered to flee its path. The storm also spawned tornadoes in parts of Virginia, New Jersey and Delaware. A twister destroyed 15 buildings in the popular holiday town of Lewes in Delaware. Flooding is likely to be a major problem this week. Parts of Philadelphia were heavily flooded, with water reaching street-sign levels in some areas. Flash flood warnings were issued up and down eastern and central Pennsylvania. “The rivers may not crest until Tuesday or Wednesday. This isn’t just a 24-hour event,” Pennsylvania governor Tom Corbett said on Sunday. Irene lost power in New York but continued to cause havoc as it moved north. More than 100,000 homes were left without electricity in Rhode Island. Delaware was soaked by 25cm of rain. The storm waters came on top of unusually high downpours earlier this month and have lead to fears of flooding inland as rivers burst their banks. New York’s public transport system is likely to be disrupted next week. On Sunday, transport workers waited for winds to die down before they were able to inspect train and subway lines. New York governor Andrew Cuomo said it was too early to say when normal service would be resumed. The region’s major airports were closed on Sunday and were likely to be closed for at least part of Monday as airlines waited for transport systems to be restored so passengers could reach them. Hurricane Irene Natural disasters and extreme weather United States New York Dominic Rushe guardian.co.uk