A huge influx of erroneous orders prevented the New York Stock Exchange from disseminating quotes shortly after the start of trading on Friday.
The exchange's quote delays caused some tickers to be locked, but a NYSE spokesman said trades were continuous throughout.
It was an influx of erroneous orders which were caught before they were executed, said Ray Pellecchia. He could not say where the orders came from.
Traders who declined to be identified said the interruption was caused in part by the early sell-off as well as by NYSE technology.
These are the problems that we talk about when we talk of systemic risk in the system. When everything is plugged in together, you could easily have systemic issues, said Joe Saluzzi, co-manager of trading at Themis Trading in Chatham, New Jersey.
Ted Weisberg, trader with Seaport Securities in New York, said the disruption had no impact on the market's decline, which steepened after the interruption was resolved. Major stock indexes were down more than 2 percent shortly before the closing bell.
Equities were under pressure Friday, as the S&P 500 index fell 2.5 percent <.SPX> and the Dow industrials <.DJI> lost 2.2 percent, retreating one day after the market's biggest percentage gain in more than three months.
Shares of NYSE Euronext slid 5.7 percent to $26.08 after the NYSE's parent company reported quarterly profits that exceeded estimates, and said it sold a big stake in its U.S. derivatives trading platform.
(Reporting by the Wall Street team in New York, Editing by Chizu Nomiyama)