The New York Stock Exchange halted trading Wednesday for more than three hours due to technical problems that it said were not caused by hacking.
The outage was due to "an internal technical issue" and "was not the result of a cyber breach," NYSE said on Twitter. "We chose to suspend trading on NYSE to avoid problems arising from our technical issue."
The exchange, the leading US platform for buying and selling the stocks of many of the world's largest companies, resumed trade at about 1910 GMT after having frozen all equity trading just after 1530 GMT.
The suspension came on a bruising day for US stocks, with all 30 members of the blue-chip Dow index falling.
The Dow Jones Industrial Average finished down 261.49 points (1.47 percent) to 17,515.42.
The broad-based S&P 500 dropped 34.65 (1.66 percent) to 2,046.69, while the tech-rich Nasdaq Composite Index tumbled 87.70 (1.75 percent) to 4,909.76.
Analysts attributed the rout not to the computer problems but to worries about Greece and China, where stocks have plunged more than 30 percent since mid-June.
"We had the NYSE halted but I don't think this was a factor in this decline," said Peter Cardillo, chief market economist at Rockwell Global Capital. "I think this is due to the acceleration of the turmoil in China."
The outage came shortly after United Airlines grounded planes at US airports for an hour due for what it also called a computer problem, sparking concerns of a coordinated cyber attack on major US institutions.
The Department of Homeland Security said it was investigating both incidents but so far had found no sign of malicious activity.
President Barack Obama had been briefed on the NYSE suspension, said White House spokesman Josh Earnest.
"There is no indication that malicious actors were involved," Earnest said.
Thomas Farley, president of the NYSE Group, told CNBC the technical issue appeared to be a "configuration problem" but he said it was "premature" to discuss the specific cause.
Stocks listed on the NYSE, which is owned by Intercontinental Exchange (ICE), continued to trade on other exchanges, including the Nasdaq and the BATS, the third largest US exchange.
The diffusion of trades from the once-dominant NYSE to other exchanges blunted the impact of the outage, said Gregori Volokhine, president of Meeschaert Capital Markets.
"What's extremely interesting is that there was practically no change in stocks due to the glitch," Volokhine said.
"If this had happened 12 years ago, there would have been panic."
- Banks, tech shares hit -
It was the second major US exchange outage in nearly two years. The Nasdaq froze trade for three hours in August 2013 due to technical problems.
But the second-ranked exchange threw a barb at its rival on Wednesday. "Nasdaq systems are operating normally and are trading all symbols including Tape A (NYSE) securities," it said via Twitter before NYSE trade resumed.
Especially hard-hit sectors Wednesday included banking, semiconductor companies and airlines.
Technology shares were also weak, with Apple losing 2.5 percent and Tesla Motors shedding 4.8 percent. Dow member Microsoft slipped 0.1 percent following news it will cut 7,800 jobs as it moves to reorganize its struggling phone business.
Another factor was the evolving picture for the US Federal Reserve's plan to begin raising interest rates later this year. Minutes from the Fed's June meeting showed Fed policy makers to be cautious over raising interest due to economic weakness and foreign risks.
Mace Blicksilver, director of Marblehead Asset Management, said the NYSE outage was less of a worry for investors than fears about the global economy.
"It's just a technical glitch and that happens. But the point is that investors are much more worried about what's going on in global markets," he said.
Blicksilver said global markets are in a "very precarious" place.