The Dow Jones Industrial Average slumped more than 600 points Friday as a virus outbreak that originated in China continued to widen, stoking stock investors' worries about the potential global economic fallout.
The broad sell-off erased the S&P 500's gains for January.
The index is on track for its second weekly loss and its biggest weekly decline since early August.
Airlines fell after Delta and American Airlines suspended flights to and from China. Technology stocks led the losses.
Amazon was the standout after issuing a blowout earnings report. The S&P 500 fell 1.8%. The yield on the 10-year Treasury note fell to 1.51%.