Wall Street dropped on worries about a possible downgrade of the United States' top credit rating and signs of economic weakness even as the US Congress passed on Tuesday a bill to avoid a debt default.
Global stock markets soared after the European Union and International Monetary Fund intervened to stop the Greek debt crisis spreading and support the weakened Euro.
Global stock markets closed sharply Friday amid investor fears that Greece's debt crisis could halt the global economic recovery.
United States regulators and stock exchanges are searching for answers after what is believed to be an electronic trading error set off a heart-stopping plunge in markets that rivalled the crash of 1987.