U.S. equities tumbled as a selloff in small caps and biotechnology spread, eroding a monthly gain for the Standard & Poor's 500 Index. Treasuries capped a slide in April amid a rout in European bonds that dented demand, while the dollar halted a nine-month rally.

The S&P 500 lost 1.1 percent at 4 p.m. in New York, with losses accelerating in late trading after the index slipped below its 50-day moving average. The Russell 2000 Index sank 2.5 percent, while the Nasdaq Biotechnology Index extended its five-day rout to 9.3 percent and Apple Inc. capped its worst three-day slide in 15 months. The euro rose a sixth day against the dollar, its longest rally since December 2013. Oil had its best month since May 2009, while gold erased its 2015 gain.

"The weakness is building on itself," Robert Pavlik, who helps oversee $9 billion as chief investment strategist at Boston Private Wealth, said by phone. "After the big run we've been having in the overall market, we're getting a setback here. A pullback in a market seeing a lot of volatility is going to happen from time to time."

The S&P 500 had rebounded this month, reaching a fresh record April 24, after a 1.7 percent decline in March. The advance was driven by a rally among energy companies as oil prices have surged 24 percent.

The Nasdaq Composite Index climbed 0.8 percent in April, and briefly erased its dot-com-era decline after 15 years. The Russell 2000 lost 2.6 percent in the month. The gauge has declined in four of the last five days, dropping 4 percent over the stretch.

Data Thursday showed consumer spending capped a lackluster first-quarter performance that was enough to keep the U.S. economy from shrinking, while separate reports added to evidence of an improving job market and a nascent acceleration in wage increases. Data Wednesday showed gross domestic product rose 0.2 percent in the first quarter.