New York: The New York Stock Exchange halted trading on Wednesday morning after suffering technical problems that it said were not caused by hacking.

‘The issue we are experiencing is an internal technical issue and is 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 trading equities, halted trade just after 1530 GMT (11:30 EST), freezing the buying and selling of the shares of many of the world's largest companies.

The outage came shortly after United Airlines grounded planes at US airports for an hour due for what it called a computer problem.

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 exchange planned to reopen around 1845-1900 GMT to give an hour of trade before the close. 

Farley said the technical issue appeared to be a ‘configuration problem’ but he said it was ‘premature’ to discuss the specific cause.

But 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.’

It was the second major US exchange outage sin 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. ‘Nasdaq systems are operating normally and are trading all symbols including Tape A (NYSE) securities,’ it said via Twitter.

- Stocks sink on global woes - 

The outage came on a grim day for US equities, which fell sharply on a range of concerns, including a major stock downturn in China and worries of a messy Greek exit from the eurozone.

Mace Blicksilver, director of Marblehead Asset Management, said the NYSE outage was less of a worry 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.

The Securities and Exchange Commission said it was monitoring the situation. 

‘We are in contact with NYSE and are closely monitoring the situation and trading in NYSE-listed stocks,’ said SEC chair Mary Jo White.

At 1830 GMT, the Dow Jones Industrial Average was at 17,564.65, down 212.36 points (1.19 percent).

The broad-based S&P 500 fell 28.13 (1.35 percent) to 2,053.21, while the tech-rich Nasdaq Composite Index lost 73.29 (1.47 percent) to 4,924.17.