U.S. stocks turned negative on Wednesday, and major indexes fell more than 1 percent after a regional gauge of business activity unexpectedly contracted in September.

The Institute for Supply Management-Chicago business barometer fell to 46.1 in September from 50.0 in August.

Economists had forecast the index at 52.0. A reading above 50 indicates expansion in the regional economy.

The Dow Jones industrial average <.DJI> dropped 128.02 points, or 1.31 percent, to 9,614.18. The Standard & Poor's 500 Index <.SPX> fell 13.94 points, or 1.31 percent, to 1,046.67. The Nasdaq Composite Index <.IXIC> slid 30.83 points, or 1.45 percent, to 2,093.21.

(Editing by Padraic Cassidy)