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 (11,200 U.S. dollars) 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.

"It won't be a problem to achieve economic growth for the next five years," says Prof. Ding Yuanzhu, deputy director of the Policy Advisory Department with the Chinese Academy of Governance.

"The point is that China must change its mode of economic growth, social development, living standards, environment protection and energy efficiency, if the country wants to build a xiaokang society in an all-round way."

The idea of xiaokang was first put forth by Chinese leader Deng Xiaoping in the late 1970s and early 1980s while drawing China's development blueprint.

It is the government's goal for 2020 to build a comprehensively xiaokang society, in which Chinese people are supposed to live well-off lives similar to Western developed countries.

Decades of rapid development have turned China into a "big" nation. Gross domestic product (GDP) grew 9.1 percent year-on-year to reach more than 33 trillion yuan last year and its foreign exchange reserves reached almost 2.4 trillion U.S. dollars, exceeding all other countries for the fourth straight year.

In the first half of this year, China overtook Japan as the second-largest economy in the world.

The hosting of Olympic Games and World Expo, and manned space flight project and Cheng'e lunar probe project have showcased China's economic rise and bolstered its people's pride and confidence.

Yet, China is far far from being a "strong" nation and its people are far from being "well-off."

China's per capita GDP reached more than 3,300 U.S. dollars last year, quadruple that of 2000, but the figure only gave China a 106th place in the world -- behind Armenia and ahead of Iraq.

And the years ahead look arduous for China's development.

"Changes in the world situation and the global economic crisis are reducing China's external demand, which has long been a driving force for the country's economic growth," says Zhuang Jian, senior economist at the Asian Development Bank's China Resident Mission.

"In social income distribution, there is a huge gap between urban areas and rural areas, and the gap is widening."

Zhuang argues that science and technology must play a greater role in economic growth, which currently relies too heavily on cheap labor and resources.

"In energy efficiency and environment protection, China needs to reform its GDP-focused performance appraisal system for local governments," he says.

Air pollution, traffic jams and skyrocketing housing prices are eroding contentment in big cities, despite their rapid economic growth, grand buildings and transport networks.

In rural areas, tens of millions of people still live in poverty, especially in vast western regions. A huge gap exists between the poor west and the affluent coastal areas in the country's east.

"Inadequate investment in rural infrastructure, a weak economic foundation and scarce health services have hindered rural development and the improvement of rural living standards," says Xiong Tingwei, a senior CPC official of Maguan County, in the remote southwestern Yunnan Province.

She hopes the central government will give greater support to the poor west for the next five years.

"To build a xiaokang society in an all-round way, it is vital to achieve xiaokang for China's rural areas and for China's farmers. It is a key to boosting rural incomes and achieving full coverage of the rural social security system," says Wang Xiaoguang, a research fellow at the Policy Advisory Department at the Chinese Academy of Governance.

"In reforming the income distribution system, we should not only re-divide the cake, but also divide it fairly."