Wall Street fell more than 1% in early trading on Tuesday due to a fall in oil and copper prices on concerns about the outlook for the Chinese economy.
U.S. stocks ended higher on Monday, rebounding from losses late last week with help from Apple and financial shares, but a drop in biotech shares limited the advance.
However, trading remains volatile as investors try to gauge when the Federal Reserve will raise interest rates.
The CBOE Volatility index, known as the "fear gauge", jumped 12% to 22.52, above its long-term average of 20.
"It was an extraordinarily quiet night of news and that is making the (European and U.S.) weakness even more frustrating (the selloff is very inexplicable)," J.P. Morgan said in a note issued before the start of trading.
The Fed last week kept rates at near-zero levels, citing the turbulence in a tightly linked global economy, including slowing growth in China.
Atlanta Fed President Dennis Lockhart said on Monday a rate hike later this year was still possible.
"The market is fragile as it is," said Art Hogan, chief market strategist at Wunderlich Securities in New York. "The volatility will continue until we get some clarity from the Fed and China."
At 9:48 a.m. ET (1348 GMT) the Dow Jones industrial average was down 176.58 points, or 1.07%, at 16,333.61. The S&P 500 was down 21.27 points, or 1.08%, at 1,945.7 and the Nasdaq composite was down 57.42 points, or 1.19%, at 4,771.54.
All 30 Dow components were down and all 10 major S&P sectors were lower.
The materials index's 1.61% fall led the decliners. Dow Chemical declined 1.7%, while LyondellBasell dropped 2.1%.
The dollar hit an almost two-week high against a basket of currencies on Tuesday after comments from Fed officials revived expectations that rates could still be hiked later this year.
Lockhart, a voting member of the Federal Open Market Committee, is scheduled to speak again later in the day. Fed Chair Janet Yellen speaks on Thursday.
European shares fell led lower by mining companies and a further fall in shares of German carmaker Volkswagen, which has admitted cheating on vehicle emission tests.
Shares of Volkswagen supplier BorgWarner were down 6.5% at $39.87.
Goldman Sachs fell 1.8% to $180.16 after Chief Executive Lloyd Blankfein said he had a "highly curable" form of lymphoma.
Miner and energy producer Freeport McMoRan declined 6.4% to $9.86.
Declining issues outnumbered advancers on the NYSE by 2,437 to 325. On the Nasdaq, 1,934 issues fell and 469 advanced.
The S&P 500 index showed one new 52-week high and 29 new lows, while the Nasdaq recorded six new highs and 63 new lows.