"We've taken our lead from the Asian markets who have not been impressed by the U.S. There's debate if there's going to be a recession in the U.S. I don't think there's much chance of that though," said Richard Hunter, an analyst at Hargreaves Lansdown Stockbrokers Ltd. in London.

"It's another horrible day," said Francis Lun, a general manager at Fulbright Securities in Hong Kong. "Today it's because of disappointment that the U.S. stimulus (package) is too little, too late and investors feel it won't help the economy recover."

Japan's benchmark Nikkei 225 index slid 3.9 percent to close at 13,325.94 points, its lowest close in more than two years. China's Shanghai Composite index plunged 5.1 percent, partly on worries about mainland Chinese banks' exposure to risky U.S. mortgage investments.

"People are certainly nervous about a potential recession in the U.S. spilling over to the rest of the world," said David Cohen, Director of Asian Economic Forecasting at Action Economics in Singapore.

"Maybe there's still some wariness about politicians are able to come up with a compromise and act sufficiently quickly" on a stimulus package, Cohen said. "I think the impact would be marginal anyway."

Traders also have shrugged off assurances from Federal Reserve Chairman Ben Bernanke that the U.S. central bank is ready to act aggressively—which means a likely big interest rate cut later this month—to help the sagging economy.

Some analysts predict that Asia won't suffer dramatically from a U.S. recession because increased trade and investment within Asia has made the region less reliant on the United States than in the past. Excluding Japan, 43 percent of Asia's exports go to other nations in the region, Lehman Brothers calculates, up from 37 percent in 1995.

But on Monday, uncertainty and pessimism reigned.

In Tokyo trading, exporters got hit hard, partly because of the yen's recent strength against the dollar. Toyota Motor Corp. lost 3.3 percent and Honda Motor Co. sank 3.4 percent.

Shares of Bank of China dropped 6.4 percent in Hong Kong after the South China Morning Post newspaper reported that the bank is expected to announce a "significant write-down" in U.S. subprime mortgage securities, citing unidentified sources. In Shanghai, the bank's stock declined 4.1 percent.

India's benchmark Sensex index fell 1,353 points, or 7.4 percent—its second-biggest percentage drop ever—to 17,605.35 points. At one point, it was down nearly 11 percent.

The decline hit companies across the board, with power utility Reliance Energy Ltd. falling 16.4 percent. Major software company Tata Consultancy Services Ltd. slid 7.6 percent

"A gloomy U.S. climate has affected the global markets. Even if those markets recover, it will take sometime for the recovery to reach India because today's fall has been so drastic," said Jayant Pai, of the Mumbai investment company IL&FS Ltd.

Still, Pai and others suggested that the declines could lead to a buying opportunity.

"The sell-off today takes us close to the bottom," she said.