WASHINGTON (AP) — Federal regulators yesterday put in place new rules aimed at preventing a repeat of last month's harrowing "flash crash" in the stock market.

Members of the Securities and Exchange Commission approved the rules, which call for US stock exchanges to briefly halt trading of some stocks that make big swings.

The exchanges will start putting the trading breaks into effect as early as today for six months. The New York Stock Exchange will begin today's trading session with five stocks: EOG Resources Inc., Genuine Parts Co., Harley Davidson Inc., Ryder System Inc. and Zimmer Holdings Inc. The exchange will gradually add other stocks early next week, expecting to reach by Wednesday the full number that will be covered. The plan for the "circuit breakers" was worked out by the SEC and the major exchanges following the May 6 market plunge that saw the Dow Jones industrials lose nearly 1,000 points in less than a half-hour. Under the new rules, trading of any Standard & Poor's 500 stock that rises or falls ten percent or more in a five-minute period will be halted for five minutes. The "circuit breakers" would be applied if the price swing occurs between 9.45 a.m. and 3.35 p.m. Eastern time – almost the entire trading day.

The idea is for the trading pause to draw attention to an affected stock, establish a reasonable market price and resume trading "in a fair and orderly fashion", the SEC said.

On May 6, about 30 stocks listed in the S&P 500 index fell at least ten percent within five minutes. The drop briefly wiped out $1 trillion in market value as some stocks traded as low as a penny. The disruption "illustrated a sudden, but temporary, breakdown in the market's price-setting function when a number of stocks and (exchange-traded funds) were executed at clearly irrational prices," SEC Chairman Mary Schapiro said in a statement.