The Standard & Poor's 500 Index capped its worst-ever four-day start to a year as turmoil in China spread around the world and billionaire George Soros warned that a larger crisis may be brewing.

The U.S. equities benchmark ended the first four days of 2016 lower by 4.9 percent, while the Dow Jones Industrial Average has erased more than 900 points so far this year. Selling in global equities began in China, where shares fell 7 percent after the central bank weakened the yuan an eighth day. Crude settled at a 12-year low, and copper dipped below $2 for the first time since 2009. The yen reached a four-month high and gold surged on haven demand.

Fresh concern that China's slowdown will hamper global growth has wiped $2.5 trillion off the value of global equities this year, as the nation's tolerance for a weaker currency is viewed as evidence policy makers are struggling to revive an economy that's the world's biggest user of resources. U.S. crude's tumble toward $30 a barrel heightened fears of disinflation and fueled concern that junk-rated energy producers won't be able to stay solvent.

Concern briefly eased after the China Securities Regulatory Commission announced the suspension of a new stock circuit-breaker that forced local exchanges to shut for the second day this week before the move gave way to anxiety that policy makers are struggling with how to contain the months-long turmoil in its financial markets.

The Standard & Poor's 500 Index slid 2.4 percent at 4 p.m in New York. The index is down 4.9 percent this year, its worst start in data going back to 1928. The MSCI All-Country World Index fell for a fourth day, bringing its slide this year to 5.2 percent.

China's devaluation revived the angst that sent financial markets into turmoil last summer, driving U.S. stocks to three-month lows Wednesday in a selloff led by commodity producers. Comments by Soros exacerbated market jitters after he told an economic forum in Sri Lanka today that global markets are facing a crisis and investors need to be very cautious.