The Dow industrials and the S&P 500 slid to 12-year lows on Thursday as General Motors' warning of possible bankruptcy and concerns about the banking system's fate reinforced investors' reluctance to take on risk.

* General Motors falls 15.5 percent to under $2

* The Dow Jones industrial average dropped 281.40 points, or 4.09 percent, to end unofficially at 6,594.44. The Standard & Poor's 500 Index slid 30.32 points, or 4.25 percent, to 682.55. The Nasdaq Composite Index tumbled 54.15 points, or 4.00 percent, to 1,299.59, its lowest close since March 2003.

(Reporting by Rodrigo Campos; Editing by Jan Paschal)