Concerns over global economic growth and uncertainties over prospects of Fed interest rates weighed on U.S. stock indices.

The Dow Jones Industrial Average dropped 358.04, or 2.1%, to 16990.69 (the lowest level since October). The S&P 500 lost 43.88, or 2.1%, to 2035.73 (all of its sectors declined). The Nasdaq Composite fell 141.56, or 2.8%, to 4877.49.

The leading indicators index from the Conference Board fell unexpectedly by 0.2% in July for the first time in almost two years. In June the index rose by 0.6%. Economists expected a 0.2% increase in July.

This morning in Asia Hong Kong Hang Seng dropped 2.32%, or 527.41 points, to 22,230.06. China Shanghai Composite Index lost 3.04%, or 111.47 points, to 3,552.82. The Nikkei fell 2.65%, or 530.19 points, to 19,503.33.

Preliminary data from Markit Economics showed that China Manufacturing PMI declined to 47.1 in August from July final reading of 47.8. Any reading below 50 indicates contraction. These data added to concerns over economic growth of the world's second-biggest economy.