Most of the stocks have resumed trading. NYSE did not immediately respond to a Reuters request for comment.

An update on the stock exchange's website said all systems were operational after initial outage at the opening bell.

"What appears to have happened is a technical glitch where all of my opening orders on the NYSE autocancelled even though some of them should have been fulfilled," said Dennis Dick, trader at Triple D Trading.

"They have corrected that now but this is going to be a big mess to clean up."