Signs of complacency were evident before stock markets around the world tumbled on Friday.

European shares have been on a tear this year, even with Greece seemingly edging closer to default. Doubts about China’s economy did not stop its stocks from more than doubling in the last 12 months. The United States market has been lukewarm this year, but the excitement seemed back on Thursday, after three companies carried out initial stock public offerings that rose sharply on their first day of trading.

But the good times evaporated on Friday. The day’s moves weren’t large by recent standards, but the global nature of the swoon gave traders and analysts pause. The benchmark Standard & Poor’s 500-stock index fell 23.81, or 1.1 percent, to close at 2,081.18.

The Dow Jones industrial average dropped 279.47 points, or 1.5 percent, to close at 17,826.30. At one point in the day, it was down as much as 357 points. The Dow is more or less flat for the year and down about 2.5 percent from the high, not adjusted for inflation, that it reached last month. The Nasdaq composite index fell 75.98, or 1.5 percent, to 4,931.81.