Asian stock markets opened sharply lower today, continuing a plunge that spread worldwide yesterday on worries that U.S. economic woes could turn global boom times to bust.

Japan's Nikkei-225 share index was down about 4.4 percent two hours into the trading session in Tokyo. That followed a 3.9 percent slide yesterday.

Stocks also were down nearly 5 percent in Australia, where they had tumbled 2.9 percent yesterday.

The heavy losses set a worrisome tone for trading today on Wall Street. Domestic markets, which had plunged last week on recession fears, were closed yesterday in observance of Martin Luther King Day.

The week's first trading session saw a barrage of selling in shares worldwide, in some cases the biggest declines since the 2001 terrorist attacks.

Yesterday, the German market dived 7.2 percent — the equivalent of the U.S. Dow Jones industrial average plummeting 871 points. Stocks sank 5.5 percent in Hong Kong, 7.4 percent in India and 6.6 percent in Brazil.

The pain overseas will be felt keenly by American individual investors, who have funneled large sums into foreign shares in this decade as those markets have rocketed. Foreign stock mutual funds have been among the most popular investments in many 401(k) retirement savings plans.

Analysts said pressure had been building on foreign share prices as the outlook for the U.S. economy had gone from bad to worse amid the housing crisis and rising losses on mortgages and other consumer loans at major banks.

The fear is that, despite the spectacular growth of many up-and-coming foreign economies such as China, India and Brazil, the world can't easily withstand a severe downturn in the U.S., which consumed $2.1 trillion of foreign goods and services in 2007, through November.

"If the States really goes into a serious recession, it will have knock-on effects for all other major economies," said Ruth Lea, economic adviser to the Arbuthnot Banking Group in London, where the main British market index fell 5.5 percent yesterday.

The United States' "problems are stretching out globally," said Alan Ruskin, chief international strategist at investment company RBS Greenwich Capital in Greenwich, Conn. "Clearly these markets are very vulnerable, plainly nervous and uncertainty rules."

Foreign investors apparently took little comfort in President Bush's call Friday for approximately $150 billion in tax rebates and other measures to give the domestic economy a boost. Some forecasters, including brokerages Goldman Sachs & Co. and Morgan Stanley, have said a U.S. recession is probably unavoidable.

On Wall Street, the Dow index fell 0.5 percent Friday to close at 12,099.40. It was down 4 percent for the week and has lost 14.6 percent from its record high set in October.

Many analysts warned against becoming too pessimistic about the resilience of the global economy, noting that the U.S. doesn't dominate world growth as much as it did 20 years ago, and that many foreign countries have built up wealth reserves to see them through rough waters.

The American economy accounted for about 26 percent of global economic activity in 2007, the International Monetary Fund estimates.

Even though the U.S. economy is stumbling, "I don't think it's even conceivable the world economy could go into recession (this year)," said C. Fred Bergsten, director of the Peterson Institute for International Economics in Washington, D.C.

He said he expected that the "worst case" was for real global economic growth of 4 percent this year, which would be healthy by historical standards.

European finance ministers, holding a regularly scheduled meeting yesterday in Brussels, Belgium, voiced confidence that Europe's economy could remain on a growth track despite America's problems.

"We feel comfortable with our economic situation at the moment," Jean-Claude Juncker, Luxembourg's finance minister, said at a news conference after the meeting.