Fears had begun to mount with a huge overseas sell-off that began in Asia, where big companies like Toyota, Sony and Samsung all disappointed investors with their earnings and their forecasts. The Nikkei average in Japan closed down almost 10 percent.

The tide of bad news continued as markets opened in Europe, with Britain reporting that its economy shrank in the third quarter. The pound fell to its lowest level against the dollar in five years. European shares recovered some ground in the afternoon, with the losses in Frankfurt and London pared to 5 percent at the close.

The sell-off appeared to be driven by two broad forces. First, investors are increasingly convinced that the global economy is headed for a long, painful recession. Second, hedge funds and other investors are being forced to sell their stocks and bonds to pay off investors and lenders.

By the time investors awoke in New York, they learned that Wall Street stock futures had fallen so far  including a 550-point decline in the Dow  that trading in them had been halted. A spokesman for the New York Stock Exchange had to affirm that it would indeed open for trading. Everyone was on notice that the market could fall at least 6 percent and perhaps much more.

A few minutes before trading was set to open at the New York Stock Exchange, an unusually large crowd of camera crews and reporters jostled for space in the press gallery to catch glimpses of traders at the opening bell.