The Dow dropped 2,013.7 points — 7.79% — as Boeing, Apple, Goldman Sachs and Caterpillar cut the index by at least 100 points each. The Dow ended the day at 23,851.02 and represented its single-worst day since Oct. 15, 2008, when it fell 7.87%.

The S&P 500 plunged 7.6% to 2,746.56 as investors punished financials and energy stocks. Energy names in the S&P 500, including Exxon Mobil, Hess and Marathon Oil, finished the day down more than 20%. Financial stocks ended down more than 10%. The equity benchmark suffered its worst day since Dec. 1 2008.

The Nasdaq Composite fell 7.29% to end the day at 7,950.68. 

The massive sell-off triggered a key market circuit breaker minutes after the opening bell. Trading was halted for 15 minutes until reopening at 9:49 a.m. ET. The sharp declines on Monday followed a roller-coaster week that saw the S&P 500 swing up or down more than 2.5% for four days straight.