The S&P 500 closed 12% lower on Monday, while the Dow fell 13% (or 2,999 points).

Driving the news: The sell-off accelerated during President Trump's afternoon press conference as concerns about the coronavirus outbreak's economic impact continued to grip markets.

Here's how swift and sharp the stock market's decline has been: The S&P 500 hit a record high just over one month ago. The index is now about 29% below that level.

The Nasdaq Composite, which dropped 12.3%, had its worst day in its 49-year history on Monday.

The big picture: The worst day for Wall Street in 30 years comes despite the series of aggressive measures announced by the Fed to shield the economy from coronavirus impact.

Outside the U.S., market volatility resumed around the globe as the pandemic worsened and governments ramped up efforts to contain the outbreak.

Europe's main stock index closed 4.8% lower, after dropping as much as 8%. Stocks in Hong Kong fell more than 4%.

The bottom line: Economists agree the near-halt to economic activity to prevent further spread of the coronavirus will put a big dent in U.S. growth. The question is how bad it will be. President Trump told reporters on Monday the economy "may be" heading into a recession.