U.S. stocks fell on Thursday, led by technology losses as Cisco Systems Inc's weak outlook fueled worries that economic softness will hurt profits.

Cisco's shares lost 16 percent to $20.57 after the Internet network product provider's CEO, John Chambers, cautioned about "short-term challenges" in Europe and public-sector spending. Late Wednesday, the company forecast revenue and earnings well below estimates.

On a percentage-loss basis, if Cisco closes at that level, this would be the worst one-day percentage drop since July 14, 1994, when Cisco slid 17.71 percent, according to Thomson Reuters Datastream.

Howard Silverblatt, an analyst at Standard & Poor's, said this was set to be the biggest one-day dollar loss ever for Cisco's stock.

By early afternoon, 385 million shares of Cisco had traded, making this one of the 10 busiest days in the history of the stock.

The warning from Cisco also dragged down shares of other tech heavyweights: Microsoft, down 1.7 percent at $26.48; Hewlett-Packard, down 3 percent at $42.83, and Juniper Networks, down 0.4 percent at $34.40. The drop in Cisco's stock reduced its own market value by about $21 billion in early trading, according to S&P.

The Dow Jones industrial average .DJI fell 91.27 points, or 0.80 percent, to 11,265.77. The Standard & Poor's 500 Index .SPX shed 7.73 points, or 0.63 percent, to 1,210.98. The Nasdaq Composite Index .IXIC dropped 27.85 points, or 1.08 percent, to 2,550.93.

Analysts saw the outlook as worrisome, particularly since profit growth for technology companies this reporting period has outperformed the broader S&P 500.