Trading on the New York Stock Exchange (NYSE) on Wednesday restarted after being suspended for more than three hours due to a technical fault. The NYSE has yet to give full details of the problem, but emphasized that it was not the result of a cyber hack. Other exchanges, including Nasdaq, reported no problems and were trading normally.
Earlier, United Airlines and the Wall Street Journal's website reported major technical problems. However, US Homeland Security said the issues appeared unrelated and were not the result of nefarious activity.
Shares were generally lower before the suspension, and continued to fall once full trading resumed.
The Dow Jones closed 1.5% lower, or 261 points, to 17,515, while the S&P 500 shed 1.7%, or 34 points, at 2,046. The tech-rich Nasdaq, 1.8% lower, or 87 points, ended at 4,909.
Trading was halted just after 1130am ET, prompting a NYSE statement: We're currently experiencing a technical issue that we're working to resolve as quickly as possible.
We will be providing further updates as soon as we can, and are doing our utmost to produce a swift resolution, communicate thoroughly and transparently, and ensure a timely and orderly market re-open.
The NYSE tweeted later that it was an internal technical issue, not a cyber attack.
The White House said that President Barack Obama was briefed, and the Securities and Exchange Commission said it was closely monitoring the situation.
The problem followed technical glitches at WSJ.com, the Wall Street Journal's website, and at United Airlines.
United Airlines said that a computer error had forced it to ground its flights in the US for the second time in recent weeks. The carrier blamed a network connectivity issue for the latest fault.
More than 800 United flights were delayed and about 60 were cancelled, but services were now returning to normal. WSJ.com is now operating normally.
US Homeland Security Secretary Jeh Johnson said the issues reported by United and the NYSE were apparently not related to nefarious activity.
I have spoken to the CEO of United, Jeff Smisek, myself. It appears from what we know at this stage that the malfunctions at United and the stock exchange were not the result of any nefarious actor, Mr. Johnson said.
He was less clear about the problems at WSJ.com, but noted that the site is in fact up again”.