The Dow Jones Industrial Average sank more than 1,000 points as the spread of the new coronavirus threatened wider damage to the global economy.
The drop was the worst for the index in two years and wiped out its gains so far in 2020.
Nervous investors scrambled for safety, loading up on gold, U.S. government bonds and other safe-harbor assets.
The price of oil fell sharply on expectations that demand for energy would tumble.
The Dow lost 1,031 points, or 3.6%, to 27,960. The S&P 500 fell 111, or 3.4%, to 3,225. The Nasdaq fell 355, or 3.7%, to 9,221.