Stock exchange operator Nasdaq OMX is cancelling a series of premarket trades that resulted in wild price swings in a number of stocks on Thursday, including Citigroup and Hewlett-Packard, the exchange said.

Nasdaq said in a statement it is cancelling trades in nine stocks in which trades occurred at prices that marked a swing of 10 percent or more from Wednesday’s closing prices.

“We have no comment further than our ruling,” said Robert Madden, a Nasdaq OMX spokesman.