U.S. stocks joined a worldwide selloff when markets opened Friday, with the Dow Jones industrial average down about 400 points, as a wave of anxiety about a global recession sent investors heading for the exits.

The Dow was off 4.5 percent in early trading. The Standard & Poor’s 500 index tumbled 5.2 percent and the Nasdaq composite lost 5.3 percent.

Stocks followed the lead of plunging markets worldwide, with Japan’s Nikkei index ending down 9.6 percent. European markets were down almost as sharply, with major indexes down 8 percent in France and Germany and 7 percent in London.

Markets were down 14 percent in Moscow when the exchange there suspended trading until Tuesday.

“Today might be the day where everybody throws in the towel,” said Peter Cardillo, chief market economist for Avalon Partners. “People are saying ‘I’ve had it, I can’t take it anymore; I’m selling everything.'”

Markets were so jittery early Friday that the New York Stock Exchange felt it was necessary to post a statement on its blog confirming that trading would open as normal at 9:30 a.m. Eastern Time, saying it felt it was necessary to answer widespread rumors that the opening bell would be delayed.

The NYSE also posted updated details of so-called circuit breakers, which would halt trading for certain periods of time if the Dow Jones industrial average falls 1,100 points during the trading day. It said it was posting that information with “the fervent hope we won’t need them.”

Futures trading limits were imposed before 7 a.m. Eastern Time, when Dow Jones industrial average futures were down 548 points. The futures for the S&P 500 were down 60 and Nasdaq 100 futures were down 84. Futures measure current index values against the perceived future performance and can indicate how markets open when trading begins in New York.

Economists said that even commodities were selling off. “It’s an across-the-board global liquidation of stocks,” said Art Hogan, chief market strategist at Jefferies & Co.