The Nasdaq Composite dropped 129.79 points, or 3.1%, its worst one-day percentage decline since November 2011. The Nasdaq Biotech index as well as iShares Nasdaq Biotechnology ETF dropped 5.6%.
The S&P 500 SPX ended the day 39.10 points, or 2.1%, lower at 1,833.08, falling below its 50-day moving average and dangerously close to crossing its 100-day moving average. Selling was so indiscriminate that only about 2% of 500 members of the index closed higher.
The Dow Jones Industrial Average fell 266.96 points, or 1.6%, to 16,170.22, its worst one-day percentage drop in more than two months.
The Russell 2000 index of small-cap stocks fell 32.30 points, or 2.8%, to 1,127.66. Panic-selling was evident from the jump in the volatility. The CBOE Vix index of implied volatility on the S&P 500 jumped 15% to nearly 16.