Technical problems forced the New York Stock Exchange to halt trading on Wednesday, jarring investors and traders already unnerved by recent volatility across global financial markets.

"We're currently experiencing a technical issue that we're working to resolve as quickly as possible," a representative of the exchange said in an email. "We are doing our utmost to [...] ensure a timely and orderly market reopen."

NYSE was quick to dismiss speculation that the trading disruption was caused by hacking. On Twitter, the exchange said the problem "is not the result of a cyber breach."

The shutdown was isolated to specific trading venues, and investors could still buy and sell NYSE-listed stocks on other venues, such as NYSE's own Arca exchange. NYSE is owned by Intercontinental Exchange Inc.

NYSE officials told Wall Street executives that the firm had no timetable for when trading would resume, according to a person briefed on a call the exchange held with industry executives late Wednesday morning.

The exchange officials told the executives that the technical glitch that disrupted trading began when NYSE attempted to fix issues affecting a smaller number of stocks, the person said. The efforts to fix that problem led to the broader trading halt.

Speaking on a late morning conference call arranged by the Securities Industry and Financial Markets Association, a trade group, NYSE officials said they would take their time to resolve the issue, said the person. The call drew about 80 market participants, including bank executives and big investors.

The suspension came in the middle of a broad selloff in U.S. stocks that was spurred by a deepening rout in China's stock markets. It comes on a day when the Federal Reserve is slated to disclose minutes from its last meeting, a release that in the past has prompted swings in stocks.

The glitch is also the latest incident illustrating the fragility of trading systems that allow capital markets to function.

While many traders were able to route stock orders to other exchanges, they're waiting to see if NYSE is able to restart trading before the market is scheduled to close at 4 p.m. New York time.

If technical problems prevent the NYSE from holding its closing auctions for NYSE-listed stocks, it could hurt big investors because they tend to do most of their trading during the opening and closing of the markets. Prices of mutual-fund shares are set by closing prices for stocks.

"The real issue is going to be can we get fixed in time for the closing auction today?" said James Angel, a professor who studies the structure of the stock market at Georgetown University.

NYSE told floor traders that the problem originated in a software update it installed last night, according to Peter Costa, a floor trader and president of Empire Executions.

"They told us they did some software updates overnight and tested it without problems, but this morning something happened," Mr. Costa said.

NYSE executives told them that they expected trading to be restored "soon," he said. A NYSE spokeswoman was not immediately available to comment on the source of the glitch.

Before the full trading suspension, NYSE officials told brokers they were investigating a "reported issue with a gateway connection" affecting trading in some 200 stock symbols, according to emails reviewed by the Journal, including the shares of Dr Pepper Snapple Group Inc., Federated Investors Inc. and Time Warner Cable Inc.

The "gateway" is a network of computers that institutions and traders use to connect to the system that matches buyers and sellers.

When the NYSE temporarily suspended trading in all stocks on Wednesday morning, trading at Seaport Securities Corp., with operations on the NYSE floor, didn't stop. Instead, orders were redirected to the firm's operations at 60 Broad Street, just down the street from the exchange.

"It's an inconvenience, it's annoying, but it has not interrupted our business," said Ted Weisberg of Seaport Securities. "It could be nothing more than a simple glitch," he said, but added that people "tend to think the worst" when something comes off the rails.

"We are in contact with NYSE and are closely monitoring the situation and trading in NYSE-listed stocks," Mary Jo White, chairwoman of the Securities and Exchange Commission, said in a statement. "While NYSE is working to resolve the situation, NYSE and NYSE MKT stocks continue to trade normally through other trading venues."

U.S. stock market malfunctions have plagued exchanges over the past several years. The biggest outage hit Nasdaq in August of 2013, when a technical problem prevented it from accurately condensing and broadcasting the best bids and offers for Nasdaq-listed stocks. Their system, one of three Securities Information Processors for the stock market, went down for three hours on August 22. Nasdaq halted all trading of Nasdaq-listed stocks during the period, which caused a major disruption for investors.

On Wednesday, Nasdaq said its systems were operating normally and were trading all securities, including those listed on the NYSE.

BATS Global Markets Inc., another major exchange operator, had an issue with one of its markets on Monday. Trading was halted on its EDGX exchange for 30 minutes.

In 2012, a technical error by Knight Capital Group led it to send a stream of incorrect orders into the market. The mistake cost it more than $450 million and laid the groundwork for the firm to be acquired by Getco LLC, a high-frequency trading firm, several months later.

BATS was forced to cancel its own initial public offering in March 2012 because of a technical issue on its exchange.

Justin Baer contributed to this article.

Write to Saumya Vaishampayan at saumya.vaishampayan@wsj.com and Bradley Hope at bradley.hope@wsj.com

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