Wall Street tumbled more than 2 percent on Tuesday and the Nasdaq turned negative for the year as Japan's looming nuclear crisis looked set to thrust financial markets into a period of turmoil.

U.S. shares seen as exposed to the disaster as well as economically sensitive stocks plunged.

The Dow Jones industrial average dropped 259.97 points, or 2.17 percent, to 11,733.19. The Standard & Poor's 500 Index fell 31.68 points, or 2.44 percent, to 1,264.71. The Nasdaq Composite Index lost 69.97 points, or 2.59 percent, to 2,631.00.

A Japanese nuclear power plant sent low levels of radiation floating toward Tokyo, prompting people to flee the capital and others to stock up on essential supplies.

(Editing by James Dalgleish)