The S&P 500 and Dow both fell more than 3 percent on Thursday, with investors worried about the outlook for the U.S. economy and the debt crisis in Europe.

The Dow Jones industrial average <.DJI> was down 351.48 points, or 2.95 percent, at 11,544.96, after briefly falling 3 percent. The Standard & Poor's 500 Index <.SPX> was down 42.05 points, or 3.34 percent, at 1,218.29. The Nasdaq Composite Index <.IXIC> was down 94.45 points, or 3.51 percent, at 2,598.62.

(Reporting by Caroline Valetkevitch)