Caterpillar Inc.'s warning that the housing slump was infecting the wider economy sent U.S. stocks tumbling by the most in more than two months on Friday, spooking investors on the 20th anniversary of the 1987 market crash.

Based on the latest available data, the Dow Jones industrial average was down 366.94 points, or 2.64 percent, to end unofficially at 13,519.83. The Standard & Poor's 500 Index was down 39.45 points, or 2.56 percent, to finish unofficially at 1,500.63. The Nasdaq Composite Index was down 74.15 points, or 2.65 percent, to close unofficially at 2,725.16.

For the week, the Dow fell 4.1 percent, the S&P lost 3.9 percent and the Nasdaq shed 2.9 percent.