ATLANTIC CITY, New Jersey (AP) — Hurricane Sandy wheeled toward land as forecasters feared today, raking major cities along the U.S. East Coast with rain and wind gusts, flooding shore towns and threatening to cripple Wall Street and New York City's subway system with a huge surge of corrosive seawater. By midday, the storm was picking up speed and was expected to blow ashore in New Jersey early in the evening, hours sooner than previously expected. Forecasters warned it would combine with two other weather systems — a wintry storm from the west and cold air rushing in from the Arctic — to create an epic superstorm. The potential for havoc stretched over 800 miles (1,280 kilometers) from the East Coast to the Great Lakes. Even before making landfall, the storm washed away a section of the Atlantic City Boardwalk in New Jersey. Water was splashing over the seawalls at the southern tip of Manhattan. Emergency workers rushed to the scene of a crane dangling off a 65-story luxury building in midtown Manhattan and streets were cleared as a precaution. Airports closed, and authorities warned that the time for evacuation was running out or already past. Many workers planned to stay home as subways, buses and trains shut down across the region under the threat of flooding that could inundate tracks and tunnels. Utilities anticipated widespread power failures. At the White House, President Barack Obama made a direct appeal to those in harm's way: "Please listen to what your state and local officials are saying. When they tell you to evacuate, you need to evacuate. Don't delay, don't pause, don't question the instructions that are being given, because this is a powerful storm." The center of the storm was positioned to come ashore Monday night in New Jersey, meaning the worst of the surge could be in the northern part of that state and in New York City and on Long Island. Higher tides brought by a full moon compounded the threat to the metropolitan area of about 20 million people. "Leave immediately. Conditions are deteriorating very rapidly, and the window for you getting out safely is closing," New York Mayor Michael Bloomberg told those in low-lying areas. Airlines canceled nearly 7 500 flights and Amtrak cancelled all train service cross the Northeast through Tuesday. As rain from the leading edges began to fall over the Northeast on Sunday, hundreds of thousands of people from Maryland to Connecticut were ordered to leave low-lying coastal areas, including 375,000 in lower Manhattan and other parts of New York City, 50,000 in Delaware and 30,000 in Atlantic City, New Jersey, where the city's 12 casinos shut down for only the fourth time ever. Obama declared emergencies in Massachusetts, Connecticut, Rhode Island, New York, New Jersey and Pennsylvania, authorizing federal relief work to begin well ahead of time. He promised the government would "respond big and respond fast" after the storm hits. Obama and Republican Mitt Romney called off their campaign events at the height of the presidential race, with just over a week to go before Election Day. Early voting was canceled Monday in Maryland and Washington, D.C. Authorities warned that New York could get hit with a surge of seawater that could swamp parts of lower Manhattan, flood subway tunnels and cripple the network of electrical and communications lines that are vital to the nation's financial center. Major U.S. financial markets, including the New York Stock Exchange, Nasdaq and CME Group in Chicago, planned a rare shutdown Monday. The United Nations also shut down. New York shut down all train, bus and subway service Sunday night. More than 5 million riders a day depend on the transit system. Boston, Philadelphia and Washington, D.C., also shut down their transit systems. Authorities moved to close the Holland Tunnel, which connects New York and New Jersey, and a tunnel between Manhattan and Brooklyn.