Trading in all symbols was halted on the New York Stock Exchange floor Wednesday due to an apparent technical issue. The NYSE tweeted that there was no sign of a cyberattack.
"The issue we are experiencing is an internal technical issue and is not the result of a cyber breach," the exchange tweeted. "We chose to suspend trading on NYSE to avoid problems arising from our technical issue."
Trading stopped around 11:30 a.m. ET.
Two U.S. officials told NBC News there was no indication the NYSE shutdown was related to the computer issue that temporarily grounded all United Airlines flights on Wednesday morning. They also said there was no indication of a cyberattack.
Trader Mark Otto of J. Streicher & Co in New York told Reuters from the NYSE floor that the mood was calm despite the unexpected shutdown.
"It's under control. We're just waiting for word. There's no sign of panic at all," he said. "We're waiting to hear word on if there's going to be a reopening, and when it is or any more details."
The NYSE said all open orders would be canceled, according to Reuters. The issues seemed to be limited to the NYSE floor, and the exchange said it did not affect the NYSE Arca and NYSE Amex/Arca Options.
RELATED: Art Cashin: Here's what to do after halt ends
The Nasdaq reported no technical issues and said it continues to trade NYSE-listed stocks.
Just after 8 a.m. ET on Wednesday morning, the NYSE put out an alert about "a reported issue with a gateway connection" affecting certain symbols. It put out a notice at 10:37 a.m. ET that the problem was resolved.
"It's been a little bit of a bumpy day. We had some technical problems even before the opening," said Art Cashin, director of floor operations at the NYSE, in a CNBC interview.
"This will not cause a move in any particular direction, so I would kind of wait it out and see what happens," he added.
A complete interruption of trading on the exchange due to a technical issue "has little precedent," the New York Times reported. The NYSE website lists seven closures since the founding of its predecessor exchange in 1817 related to world-changing events, including the assassination of President Abraham Lincoln and the terrorist attacks on Sept. 11, 2001.
This is a breaking news story. Refresh for updates.