The S&P 500 fell to a new low for the year on Wednesday as service sector growth was less robust than expected in July, another discouraging sign for the economy.

The session has been volatile, with equities initially higher as traders sought to halt the longest losing spell for stocks in almost three years, and data showed a stronger-than-expected labor market as well as a slowdown in the services sector.

The Dow Jones industrial average was down 47.87 points, or 0.40 percent, at 11,818.75. The Standard & Poor's 500 Index was down 5.06 points, or 0.40 percent, at 1,248.99. The Nasdaq Composite Index was down 11.55 points, or 0.43 percent, at 2,657.69.

(Reporting by Ryan Vlastelica)