U.S. stocks fell, extending the worst weekly slump in the Standard & Poor’s 500 Index since November, after Warren Buffett said the economy “has fallen off a cliff” and the World Bank predicted a global contraction.

Hewlett-Packard Co., DuPont Co. and Verizon Communications Inc. slumped 4 percent or more. Merck & Co. sank 7.7 percent, dragging down the Dow Jones Industrial Average, after agreeing to buy Schering-Plough Corp. for $41.1 billion. Aflac Inc., the largest provider of supplemental insurance, dropped 15 percent after UBS AG recommended selling the shares.

The S&P 500 fell 1 percent to 676.53, the lowest level since September 1996. The index, which decreased as much as 1.5 percent and climbed 1.7 percent, swung between gains and losses at least 25 times. The Dow average retreated 79.89 points, or 1.2 percent, to 6,547.05.

(Bloomberg.com)