The Federal Reserve cut its key interest rate by three-quarters of a percentage point to 3.5 percent, its biggest in more than 23 years. But markets paused only momentarily before the selling wave renewed as investors seem fixated on the idea that the U.S. will drag the world economy down.

"Incoming information indicates a deepening of the housing contraction as well as some softening in labor markets," the Fed said. Canada's central bank cut too.

U.S. Treasury Secretary Henry Paulson said he was confident in the resilience of the U.S. and global economies and welcomed the Fed cut as a helpful move.

"This is very constructive and I think it shows this country and the rest of the world that our central bank is nimble and can move quickly in response to market conditions," Paulson said.

The White House, rushing to put together a $150 billion stimulus package to prop up an economy ravaged by a housing slump and a mortgage defaults crisis, declined immediate comment on the Fed cut.

President George W. Bush was set to meet members of Congress later in the day to discuss the economic rescue package.

Outside North America, politicians and central bankers said the market selloff looked excessive. But they had their work cut out to convince as people like billionaire investor George Soros, who said the world faced a financial crisis worse than any since World War Two.