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Stock markets in the United States traded in a volatile session, with the Standard & Poor’s 500-stock index closing down nearly 4 percent.

In China, the benchmark Shanghai composite index erased all of the gains it had made this year.

Many investors sought refuge from the upheaval by turning to American and European government bonds.

In Europe, stocks fell sharply, with the main indexes down by 4 percent or more in the early afternoon.

The market drops have erased nearly $10 trillion from the global stock market since a peak on June 3.

The American and international oil benchmarks have fallen to their lowest point in more than six years.

In-Depth

Stocks in the United States tumbled on Monday morning as another sell-off that started in China roiled markets around the world.

Immediately after the opening bell in New York, the Dow Jones industrial average dropped more than 1,000 points, or more than 5 percent — one of the most precipitous such plunges in recent years. Within an hour, though, American stocks had made up much of their earlier losses and the Dow was down about 2 percent.

Investors’ concerns over China’s economic slowdown and a souring view of emerging economies have rattled financial markets around the world in recent days, and showed no signs of letting up.

“There was a huge amount of negative sentiment built in this morning,” said Dan Greenhaus, the chief global strategist at BTIG.

Mr. Greenhaus said that many investors ended last week hoping that the Chinese government would step in over the weekend to announce some steps to support the markets, but nothing significant was announced, contributing to the pessimism on Monday morning.

In early trading in the United States, the benchmark Standard & Poor’s 500-stock index was initially down more than 5 percent and the Nasdaq fell more than 8 percent. But about an hour into trading, the S.&P. was down about 2 percent and the Nasdaq, 2.4 percent.

In China, the benchmark Shanghai composite index closed 8.5 percent lower on Monday, erasing all of the gains it had made in an extraordinary run-up this year. And in Europe, stocks fell sharply, with several of the main indexes down by 6 percent or more in late-afternoon trading.

The meltdown, which has erased nearly $10 trillion from the global stock market since a peak on June 3, poses a challenge to the Federal Reserve in the United States. The central bank’s chairwoman, Janet L. Yellen, and her colleagues on the Fed’s policy board have been warning investors for months that the central bank was moving toward the first increase in its main interest rate since it was cut to zero in December 2008.

Many analysts have said that a correction to stock market valuations was overdue after a long bull market. And it is too early to say how the financial market slump will affect the underlying global economy where goods and services are actually produced and consumed.

Many of the world’s central bankers will have a chance later this week to compare notes and discuss whether new policy steps are needed when they gather, along with finance ministers and academics, in Jackson Hole, Wyo., for the Federal Reserve Bank of Kansas City’s annual conference.

Commodities also slumped on Monday. Futures for Brent and United States crude oil fell to their lowest point in more than six years on concerns about possible weaker demand from Asia amid a general oversupply. Contracts for the European benchmark Brent crude fell 3.7 percent to $43.80 — its first time below $45 since March 2009.

The selling in China has accelerated despite extraordinary government intervention in the last two months aimed at propping up share prices. As the slide on Monday highlighted, those efforts have not been a success and the damage has been felt far beyond the Chinese market. The gloom was shared across Asia. In Japan, the Nikkei 225 stock average closed 4.6 percent lower, while Australia’s main index fell 4.1 percent.

In Hong Kong, where the Hang Seng Index closed 5.2 percent lower, the mood at brokerage firms was grim.

“People who had wanted to bottom feed by buying earlier this morning are all losing money,” said Andy Wong, a Hong Kong stockbroker. “The market trend does not look good, it is all bad news, globally. All the markets are going down, globally; the Chinese stock markets are in free fall today.”

Leung Chung, a 62-year-old retiree and day trader in a T-shirt and with a toothpick in his mouth, looked sourly at the monitors at his local brokerage firm in late morning. “I just purchased some stocks earlier this morning, but have already lost money,” Mr. Leung said. “I am not too concerned as I only bought stocks with solid financial strength.”

The dollar rose against most Asian currencies, with the exception of the yen, which is considered a regional haven. The dollar fell 1.5 percent to 120.18 yen.

The euro gained 0.9 percent against the dollar, trading at $1.1491.

Lee Hardman, a currency analyst at Bank of Tokyo-Mitsubishi UFJ in London, said in a research note that the rising euro and yen were “creating a policy headache for the European Central Bank and Bank of Japan,” as well as for the Fed.

Stronger currencies, he said, would make it harder for central banks to fight deflationary pressures. He noted that long-term forecasts for the eurozone showed inflation beginning to return to the levels that existed before the European Central Bank began its bond-buying program this year.

The rout has deepened globally as uncertainties have increased over the health of China’s economy, previously a major engine of global growth. The surprise devaluation on Aug. 11 of China’s currency, the renminbi, was the biggest drop since the country’s modern exchange rate system was established in 1994.

The move raised concerns that China’s slowdown was worse than it had previously appeared to be, a development that would have far-reaching effects, given China’s increasing economic importance to Asia and the rest of the world.