In Europe, the Stoxx 600 Index slid 1 per cent, as did France's CAC 40. The UK's FTSE 100 gave up 0.8 per cent, while Germany's DAX dropped 0.9 per cent.
"We are scared about a slowdown in China," Paolo Vicentini, who is responsible for total return strategies at Edmond de Rothschild in Milan, told Bloomberg News. "If the economy does not keep growing at the same pace, companies in key European countries like Germany which depend on Chinese demand will suffer."
The latest US economic data were a mixed bag. The preliminary US PMI fell to 53.7 this month, down from 55.0 in December, according to Markit.
"The flash PMI indicates that the manufacturing sector continued to grow at the start of 2014, and that the underlying trend most likely remained reassuringly robust," Chris Williamson, chief economist at Markit, said in a statement.
Separately, jobless claims rose by 1,000 to 326,000 last week, less than the 330,000 economists had expected, while sales of previously owned homes increased 1 per cent in December to a 4.87 million annual pace. Sales for 2013 were the highest since 2006.
"We lost some momentum toward the end of 2013 from disappointing job growth and limited inventory, but we ended with a year that was close to normal given the size of our population," Lawrence Yun, NAR chief economist, said in a statement.
In the euro zone, both consumer confidence and manufacturing output rose more than expected in January, according to separate reports released today.
The latest US earnings offered both disappointment and reasons for optimism. Netflix did the latter, boosting its shares by 15.9 per cent, as the company's outlook surpassed expectations.
Shares of American Eagle Outfitters tumbled, however, last 9.1 per cent weaker, after the company announced that its CEO is leaving.