When night falls, a middle-aged man walks slowly toward a trash bin near the busy Xuanwumen intersection in downtown Beijing, and looks around before swiftly taking out an empty plastic bottle and then moving on to the next bin.

His tidy clothes and behavior suggest he is neither a street cleaner nor a scavenger from outside the Chinese capital, but a local resident of a low-income family who hopes to make some money through collecting recyclable bottles.

He does it at night to avoid being spotted by neighbors or acquaintances.

He refuses to speak and looks away awkwardly.

Behind him, in a luxury high-rise, apartments are selling for 75,000 yuan (US$11,200) per square meter -- equivalent to a year's salary for a young white-collar worker and at least 30 years' income for a rural family in the country's poor western regions.

For the world's most populous nation and the second largest economy, the widening wealth gap is an obvious obstacle on the road to a "xiaokang" -- moderately prosperous -- society.

That poses grave challenges for Communist Party of China (CPC) leaders, who gathered Friday in Beijing to discuss the formulation of China's 12th Five-Year Program (2011-2015).

Narrowing the gap and reforming the income distribution system will undoubtedly be a focus of the four-day Fifth Plenary Session of the 17th CPC Central Committee, as the next five years are considered a key period for building a xiaokang society.