Stocks tumbled at the open on Thursday, with the S&P 500 and the Nasdaq falling more than 3 percent on concerns that the European debt crisis might spread to the U.S. banking sector.

The Dow Jones industrial average was down 317.00 points, or 2.78 percent, at 11,093.21. The Standard & Poor's 500 Index was down 37.87 points, or 3.17 percent, at 1,156.02. The Nasdaq Composite Index was down 92.33 points, or 3.68 percent, at 2,419.15.

The New York Stock Exchange and NYSE Amex Cash Markets invoked a rule to smooth trading, also known as Rule 48, at the open on Thursday.

(Reporting by Ashley Lau)