Stocks plunged in the final hour of trading Thursday, sending the Dow Jones industrial average down more than 675 points, or more than 7 percent, to its lowest level in five years after a major credit ratings agency said it was considering cutting its rating on General Motors Corp.
The Standard & Poor's 500 index also fell more than 7 percent.
The declines came on the anniversary of the closing highs of the Dow and the S&P. The Dow has lost 5,585 points, or 39 percent, since closing at 14,198 a year ago. The S&P 500, meanwhile, is off 655 points, or 42 percent, since recording its high of 1,565.15.