Stocks slumped on Wall Street, after markets in Europe were buffeted by worries that the Greek debt crisis would prove contagious and Chinese investors endured another topsy-turvy session.

The Dow Jones industrial average closed down 2 percent, the Standard & Poor’s 500 was down 2.1 percent, and the Nasdaq fell 2.4 percent. The losses wiped out all the gains for the Dow and S.&P. 500 indexes this year.

The Euro Stoxx 50 index, comprising the eurozone’s big blue chip companies, closed 4.2 percent lower, after being down about 5 percent at the opening. The FTSE 100 index in London fell 2 percent.

In Greece, banks and markets will be closed for the week, after Prime Minister Alexis Tsipras interrupted last-ditch debt negotiations early Saturday with the announcement that he was calling a referendum for July 5 on whether to accept the tough terms offered by international creditors.