Stocks are down sharply Thursday, making the prior day's strong performance seem like an aberration, as Wall Street stumbles toward what could be its worst December since the Great Depression.
The Dow Jones Industrial Average slumped 400 points in late-afternoon trading after dropping as much as 611 points earlier.
Technology companies and health care stocks, big gainers on Wednesday when the market had its best day in 10 years, took some of the heaviest losses in Thursday's broad slide. Energy companies as well as internet and social media companies also fell sharply.
Volatility has been the norm this month. The market remains on track for its worst December since 1931, during the depths of the Depression, and could finish 2018 with its biggest losses in a decade. Even with Wednesday's big gains, the Dow, S&P 500 and Nasdaq are all down more than 11 percent for the month.
"The last two days are really demonstrable of what the market is struggling with," said Tom Martin, senior portfolio manager of Globalt Investments. "It's looking for a bottom. It's looking for a reason to gain a little more confidence. And it's also looking for opportunities to reposition and lessen risk."
The partial government shutdown that began over the weekend has weighed on the market. Investors have also been unnerved by the personnel turmoil inside the Trump administration, trade tensions with China, the slowing global economy and worries that corporate profits are going to slip sooner or later.
The S&P 500 index fell 47 points, or 1.9 percent, to 2,420 as of 3:05 p.m. Eastern Time. The Dow slid 402 points, or 1.8 percent, to 22,475. Both indexes rose about 5 percent Wednesday, when the Dow had its biggest-ever single-day point gain.
The tech-heavy Nasdaq lost 153 points, or 2.3 percent, to 6,401. The Russell 2000 index of smaller-company stocks gave up 33 points, or 2.5 percent, 1,296.
Technology companies, a big driver of the market's gains before things deteriorated in October, slumped Thursday. Advanced Micro Devices lost 6 percent to $16.83.
Perrigo gave up 5.8 percent to $38.35, one of the big decliners in the health care sector.
Retailers, which rallied Wednesday on data showing holiday retail sales growth hit a six-year high, helped pull the market lower Thursday. Amazon slid 4 percent to $1,412.48.
Bank stocks fell along with Treasury yields, which affect interest rates on mortgages and other loans. KeyCorp declined 3.7 percent to $14.16 as the yield on the 10-year Treasury fell to 2.74 percent from 2.79 percent late Wednesday.
A sharp decline in oil prices weighed on energy stocks. Noble Energy slid 4.8 percent to $18.16.
Benchmark U.S. crude dropped 3.5 percent to settle at $44.61 a barrel in New York. Brent crude, used to price international oils, lost 4.2 percent to $52.16 a barrel in London.
The dollar fell to 110.77 yen from 111.36 yen on Wednesday. The euro strengthened to $1.1446 from $1.1351.
Gold edged up 0.6 percent to $1,281.10 an ounce and silver gained 1.2 percent to $15.31 an ounce. Copper fell 1.2 percent to $2.67 a pound.
The slide in U.S. markets followed a sell-off in major indexes in Europe.
In European markets, where trading resumed after a Christmas holiday break, the German DAX slid 2.4 percent, while France's CAC 40 gave up 0.6 percent. Britain's FTSE 100 fell 1.5 percent.
In Asian markets, the Nikkei 225 index rebounded 3.9 percent, while South Korea's Kospi was little changed. The Hang Seng index fell 0.7 percent and Australia's S&P-ASX 200 jumped 1.9 percent. Stocks climbed in Taiwan and throughout Southeast Asia.