PARIS — Global markets tumbled on Thursday over concern about a credit crunch in China and uncertainty about the United States central bank’s plans for withdrawing the monetary stimulus upon which the American economy has become dependent.

Just a day after the Federal Reserve hinted that it could soon begin winding down its bond-purchasing program, investors were unnerved by reports that Chinese banks had become reluctant to lend to one another, causing interest rates in the interbank market to spike to punishingly high levels.

On Wall Street, the broad-based Standard & Poor's 500-stock index ended down 2.5 percent Thursday, the Dow Jones industrial average dropped 2.3 percent — more than 350 points — and the Nasdaq composite index shed 2.3 percent. On Wednesday, the S.&P. 500 fell 1.4 percent.

The pain was also felt in the bond market, with yields on government bonds, which move in the opposite direction of the price, surging worldwide. The 10-year United States Treasury bond was yielding 2.380 percent, up 2.8 basis points. A basis point is one-hundredth of a percent. Expectations that interest rates will rise tend to depress the prices of existing securities.