Stocks fell sharply at the open today, including a drop of more than 300 points by the Dow Jones industrial average.

The Dow had fallen 335.88 points as of midmorning, a drop of more than 3 percent. The Nasdaq composite index was down 71.67 points, and the Standard & Poor’s 500 index was down 33.07 points; both of those declines were near 3 percent.

The MSCI All-Country World index had slipped 2.8 percent as of midmorning, extending declines from its May peak to more than 20 percent, Bloomberg reported.

The Federal Reserve said yesterday that it saw “significant downside risks” in the U.S. economy and that it will replace $400 billion of short-term debt with longer-term Treasuries to spur growth as the recovery falters.

“The storyline is that global growth is decelerating,” said Mike Ryan, a chief investment strategist at UBS Wealth Management Americas, in an interview with Bloomberg. “Financial stresses are rising, and policy-makers are finding few viable options to stabilize the real economy.”

The S&P 500 extended losses following a three-day, 4.1 percent decline. The index slumped 2.9 percent yesterday after the Fed’s statement and as Moody’s Investors Service cut its long-term credit ratings on Bank of America Corp. and Wells Fargo & Co., saying U.S. support will become less likely if lenders get into financial trouble.