NEW YORK — Stocks opened sharply lower Thursday, extending a rout around the world. Indicators across the financial markets suggested investors were frightened that the global economy is in for a long slump.

The Dow Jones industrial average fell 300 points within minutes of the opening bell. It fell 283 points on Wednesday after a tacit acknowledgment from the Federal Reserve that the U.S. economy won’t improve anytime soon.

The Dow and the Standard & Poor’s 500 index were both down about 3 percent. At 11:20 a.m. EDT, the Dow was down 357 points, at 10,767. The S&P fell 34 points to 1,132. The Nasdaq composite was down about 2.5 percent.

The price of commodities like oil and metals dropped steeply because investors worried that demand for them would fall if the world economy keeps slowing or falls into recession again.

Looking for a safe place to put their money, traders bought American government debt, which they see as much less risky than stocks. The yield on the 10-year Treasury note hit a record low, 1.77 percent, down from 1.86 late Wednesday. Yields fall as investors buy bonds and send their prices higher.

The Fed, adopting a new strategy to try to get the U.S. economy going, announced Wednesday that it would shuffle $400 billion of its own holdings in hopes of reducing interest rates on long-term loans.

The central bank hopes that allowing people and businesses to borrow money more cheaply will encourage them to spend it throughout the economy, providing a lift that could turn it around.

The Fed statement troubled investors. It offered a bleak assessment of the future of the U.S. economy, saying it sees “significant downside risks to the economic outlook,” including volatility in overseas markets.

“What we’re seeing is the ebbs and flows around a big risk that everyone’s having difficulty dealing with,” said Barry Knapp, head of U.S. equity strategy for Barclays Capital. “We’re just going to be dealing with these waves for some time to come.”

On the first day after the Fed announcement, economic news was bad around the world. A closely watched survey in Europe indicated a recession could be on the way, and a Chinese manufacturing survey suggested a slowdown there.

Asian stocks were hammered to start the world’s trading. The Nikkei index in Japan fell 2.1 percent. The main stock averages fell 2.9 percent in South Korea, 2.6 percent in Australia and almost 5 percent in Hong Kong.

Europe fared worse. The stock market fell 5.4 percent in France, 4.6 percent in Germany and almost 5 percent in Britain. Besides the economic headache, Europe is wrestling with how to tame a big debt problem.

In France, the CEO of BNP Paribas, a major bank, tried to calm the markets by declaring that the bank had sufficient cash. French bank stocks have been hit hard because investors are worried they hold too much Greek debt.

In New York, stocks fell sharply even though the New York Stock Exchange executed a rule designed to smooth trading.

The exchange invoked Rule 48, which limits how much information is released about stock trades. It is only used on days when extreme volatility is expected in the stock market.

Computer systems that are programmed to analyze charts, capitalize on tiny changes in price and execute trades with no human intervention have made the swings in the market bigger this summer.

High-frequency trading programs make up about half of the trading volume in a normal market day but 70 percent or more on a volatile one.

The price of oil fell 6 percent, more than $5 a barrel, to $80.76, its lowest since Aug. 19. The selling reflected concerns that world demand for oil would fall if the economy slows.

And the price of gold fell more than 4 percent. Earlier this summer, gold set one record high after another. Investors wanted it both as a safe place for their money and to cash in on what seemed an unstoppable run.

The government reported Thursday that fewer Americans filed new claims for unemployment benefits last week. But the decline wasn’t nearly enough to raise any real hope that the job market is getting better.

FedEx stock fell 9 percent after it said that it would earn less in 2012 than it had expected. The company is seen as an indicator because demand for shipping rises and falls with the economy.

The next big round of corporate earnings reports doesn’t start for several weeks, but many analysts expect big companies can’t sustain the strong profits they have posted for the last few quarters.

The S&P 500, a broad measure of the stock market, is still above its lowest point from August — 1,119 on Aug. 8. Major swings in the market were common last month as investors focused on fear of a new recession.