According to a spokeswoman, trading was set to reopen at 8:15 a.m. PDT, but the exchange missed the deadline. Trading resumed at 8:35 a.m. NYSE Chairman Richard Grasso, appearing on CNBC, had said he was confident the exchange would open on time.
The NYSE said half its trading floor was unable to complete transactions at the opening bell, so it took the entire exchange offline around 7 a.m. until the problem could be fixed.
"We lost connectivity between our data sites and the trading floor," the NYSE said in a statement posted on its Web site. "We could have continued trading with other than our systemic traffic, but did not feel this was fair, particularly to the retail investor."
Many of the stocks traded on the exchange, including 10 of the 30 Dow Jones industrial average components, did not begin trading at the opening bell Friday morning.
NYSE representatives weren't immediately available to comment. Grasso said the exchange shut down because only half of the stocks were trading. The move was made "in the interest of all market participants."
Because of an overnight software change, institutional traders were allowed to trade, but not individual investors. He did not state what software was involved. There was some light trading before the shutdown, with about 63 million shares changing hands.
The Chicago Mercantile Exchange said it halted trading in its Standard & Poor's 500 stock index futures contracts and the S&P MidCap 400 futures contracts at 7:30 a.m. because of the NYSE problems.
Grasso said the NYSE shut down six years ago for a major technical glitch.
The outage follows a similar problem at the Nasdaq exchange earlier in the week. That exchange shut down for 20 minutes at the start of the day. The Nasdaq was working to increase capacity on its system when the problem occurred.