The income gap between the rich and poor in China has surpassed that of the U.S. and is among the widest in the world, a report says, adding to the challenges for President Xi Jinping as growth slows.

A common measure of income inequality almost doubled in China between 1980 and 2010 and now points to a "severe" disparity, according to researchers at the University of Michigan. The finding conforms to what many Chinese people already say they believe — in a 2012 survey, they ranked inequality as the nation's top social challenge, above corruption and unemployment, the report showed.

The growing wealth disparity that accompanied China's breakneck growth in the decade through 2011 has increased the risk of social instability in the world's most populous nation. Xi is engineering a slowdown in economic expansion to below 8 percent and leading a campaign against corruption as he grapples with rising unrest, credit risks, and pollution choking the country's biggest cities.