U.S. stocks plunged to lowest levels since last October after a rout in Chinese stocks triggered a world-wide selloff of risky assets such as equities. The Dow Jones Industrial Average DJIA, -1.84% dropped 1000 points, or 6%, to 15,441. The S&P 500 SPX, -1.15% opened 100 points, or 4.9%, lower at 1,874. The benchmark index is down more than 10% from its peak reached on May 21. The Nasdaq Composite COMP, -0.13% began the day down 360 points, or 7.6%, to 4,349.