U.S. stocks plunged on Thursday afternoon before recovering some ground, with the Nasdaq at one point down more than 9 percent and the S&P 500 and Dow briefly falling into negative territory for the year, as worries about contagion from Greece's debt problems mounted.

The Dow Jones industrial average <.DJI> was last down 382.03 points, or 3.52 percent, at 10,486.09. The Standard & Poor's 500 Index <.SPX> was down 43.57 points, or 3.74 percent, at 1,122.33. The Nasdaq Composite Index <.IXIC> was down 91.08 points, or 3.79 percent, at 2,311.21.