U.S. stocks tumbled Wednesday, with the Dow closing at lows last seen in late July, as coronavirus cases surged globally and investors worried about the possibility of a contested U.S. presidential election next week.

The spiraling pandemic and Washington's failure to reach a deal on new fiscal stimulus before the November election drove all three stock indexes to close more than 3 percent lower in heavy trade.

The sell-off accelerated during the session's final minutes, with both the Dow and benchmark S&P 500 posting their biggest single-day declines since June 11.

The Dow Jones Industrial Average plunged 943.24 points, or 3.43 percent, to 26,519.95. The S&P 500 decreased 119.65 points, or 3.53 percent, to 3,271.03. The Nasdaq Composite Index shed 426.48 points, or 3.73 percent, to 11,004.87.

All the 11 primary S&P 500 sectors sank, with technology and energy down 4.33 percent and 4.22 percent, respectively, leading the losses.

U.S.-listed Chinese companies traded lower, with all of the top 10 stocks by weight in the S&P U.S. Listed China 50 index ending the day on a downbeat note.

The Cboe Volatility Index, widely considered as the best fear gauge in the stock market, surged 20.78 percent to 40.28.

Twelve U.S. states set records for hospitalized COVID-19 patients, while Germany and France announced plans to shut large swathes of public life for a month as the pandemic surged across Europe.

Nationwide daily cases have risen by an average of 71,832 over the past week, according to a CNBC analysis of data from Johns Hopkins University.

More than 8.8 million COVID-19 cases have been reported in the United States, with the death toll topping 227,000 as of Wednesday afternoon, according to a tally by the university.

Shares of hotels, airlines and other leisure-related companies sensitive to COVID-19-related turmoil sank, with the S&P 1500 airlines index falling 4.3 percent. The energy index slid 4.2 percent as oil prices tumbled on fears of a deeper drop in fuel demand.

"Uncertainty about COVID-19-related mobility restrictions and U.S. politics mean we should expect volatility to remain elevated for the balance of the year," chief investment officer at UBS Global Wealth Management Mark Haefele said in a note.

(With input from agencies)