Across the northeastern US, 26 people were confirmed dead, and 7.5 million were beginning their second day without electricity."This was a devastating storm, maybe the worst New York City has ever experienced," tweeted Mayor Michael Bloomberg. "The impacts will be felt for some time.""Our state woke up today to absolute devastation," said Governor Chris Christie of next-door New Jersey state. "There are no words to describe what's been New Jersey's experience over the last 24 hours, and what we'll have to contend with over the coming days, weeks and months."For the second day in a row, all major stock markets were closed.The storm weakened as it moved further inland but forecasters still warned of gale-force winds and flooding along the densely-populated coast, where 7,400 National Guardsmen were mobilised in 11 states to provide emergency relief.Airlines scrapped one in five scheduled US flights Tuesday, after Sandy flooded New York's airports and spawned disruptions rivalling the toll from recent blizzards.The former hurricane, now termed a post-tropical cyclone, grounded 6,117 US flights, or 20 per cent of the day's total, according to data compiled by industry researcher FlightAware. All three of New York's main airports shut down for a second day on Tuesday, paralysing the nation's busiest air-travel market.Mayor Bloomberg said New York's subways may not open for five days. Governor Christie said restoring train service to Manhattan could take as long as 10 days.Crews began clearing downed trees and branches, and street cleaners scrubbed muck from roads. Power crews in trucks set about trying to re-illuminate the city of 8 million, the most populous in the US.Sandy, which weakened as it passed over the coast, is among the worst storms in New York history, rivaling the blizzards of 1888 and 1947. It was the worst disaster in 108-year history of the subway system and exceeded transit officials' worst-case scenario, said Joseph Lhota, chairman of the Metropolitan Transportation Authority.Subway service may be out for as long as four to five days after "extensive flooding" affected all tunnels, said the mayor.President Barack Obama has declared a "major disaster" in New York and New Jersey states. This clears the way for federal grants and loans to help storm victims acquire temporary housing and repair damage.Seawater coursed between the iconic skyscrapers of New York's financial district in lower Manhattan, flooding subways and road tunnels and shorting out the power grid, leaving a half-million households and businesses in the dark.Further south, giant waves crashed over vast swathes of the eastern seaboard, turning coastal cities into ghost towns as the high winds grounded flights and shut down rail links, public transport and government offices.The catastrophe completely overshadowed the US election race, forcing a halt to campaigning a week before Americans were due to go to the polls to choose between Obama and his Republican challenger Mitt Romney.