U.S. stocks tumbled on Monday, with the Dow Jones Industrial Average dropping to an 18-month closing low in a tumultuous trading session that saw the blue-chip benchmark briefly plummet more than 1,000 points.

The Dow plunged as much as 1,089 points in the first six minutes of trading before paring losses as traders said mutual funds and other investors began stepping in to buy up beaten down stocks. More than 13.9 billion shares changed hands, making Monday the largest volume day since August 2011.

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