NEW YORK -- The New York Stock Exchange said Friday it instituted upside trading curbs at 9:37 a.m. as U.S. stocks rose sharply in early trading.

The U.S. market's surge followed a surprise cut in the U.S. Federal Reserve's discount rate before the market open. The rate governs direct Fed loans to banks.

The New York Stock Exchange Composite Index , which is used to determine when to begin trading curbs, was up 235.49 points, or 2.6 percent, at 9322.59.

The trading curbs require that all program buying of S&P 500 stocks must be on a down-tick.

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