U.S. stocks posted the biggest two-day surge since 2009 as a relief rally swept across global markets and the economy grew stronger than expected in the second quarter.

The Standard & Poor’s 500 Index briefly pared gains in late afternoon trading, trimming an advance of as much as 2.5 percent to less than 1 percent before resuming its climb, indicating markets are still vulnerable to violent swings. The gauge rose 2.4 percent to 1,987.73 at 4 p.m. in New York, capping its best back-to-back advance since the bull market began more than six years ago.

“We got our pullback, and now we’re going to focus on U.S. things like GDP and the Fed,” said John Canally, chief economic strategist at LPL Financial Corp. in Boston. “When you’re in a correction, it’s not fun, but when you’re out, you can refocus on what matters.”

Data today showed gross domestic product rose at a 3.7 percent annualized rate, exceeding all estimates of economists surveyed by Bloomberg, and up from the 2.3 percent reported last month. Bigger gains in consumer and business spending showed the U.S. expansion getting back on track. A separate report showed filings for jobless benefits declined to a three-week low.

Contracts to purchase previously owned homes climbed in July for the sixth time in the last seven months, another report showed. The 0.5 percent increase in the pending home sales index was less than a 1 percent rise forecast by economists surveyed by Bloomberg.

“The economy is in good shape and we’re chugging along at a good pace and that’s good for earnings,” Canally said. “It also should clear some of the noise out of this market. There has been a lot of concern about a slowdown in the economy.”

The data come as Federal Reserve policy makers debate whether growth is strong enough to withstand the first increase in the benchmark interest rate since 2006. Additionally, the global plunge in stocks also could argue for a delay.

Fed Watch

Market turmoil sparked by growth concerns has reduced expectations for the Fed to increase interest rates as soon as next month. New York Fed Bank President William Dudley said Wednesday the upheaval has made the case for raising rates in September “less compelling.”

Traders are pricing in a 30 percent chance the central bank will act at its next meeting, down from almost even odds before China’s surprise currency move earlier this month.

China’s Shanghai Composite Index jumped 5.3 percent amid a late-session surge. People familiar with the matter said the government stepped in to boost its stock market, reassuring investors of the state’s support.

Investors will seek further clues on an impending rate increase from an annual symposium at Jackson Hole, Wyoming starting today. Central bankers gather there for an academic discussion on inflation just as China’s slowdown renews fears of falling prices. Fed Chair Janet Yellen won’t attend this year.