China's drive for urbanization faces environmental and economic pressures as the government pledges reforms to promote social change, experts say.
With over 52 percent of China's 1.3 billion people now living in cities, the government's efforts to improve air quality and advance sustainable development may be critical to its urbanization drive.
Thick smog has been choking many of China's cities over the past two months, challenging the benefits of moving from rural areas for a better quality of life.
At its recent plenary session, the ruling Chinese Communist Party backed plans to "endow peasants with more property rights," potentially helping migrants gain the social advantages of city dwellers.
Moves to reform the "hukou" system of household registration could mean access to urban services like health care and education for some 20 million new residents a year.
But many of the industries that China needs to expand its cities have also been targeted as sources of pollution and unsustainable development, posing a tangle of problems.
"The pace of urbanization is what's driving the consumption of cement, glass, steel, aluminum and all the things that go into building these enormous infrastructures," said Mikkal Herberg, director of energy security research for the Seattle-based National Bureau of Asian Research (NBR).
The construction-related industries are China's leading consumers of power and coal, making them primary sources of pollution.
In September, the Ministry of Industry and Information Technology placed steel and cement on a list of 13 sectors that must cut overcapacity and close power-wasting plants by the end of the year.
The order follows the government's five-year action plan to reduce smog and coal-burning in urban areas by 2017.
In October, the State Council also cited steel and cement along with flat glass, electrolytic aluminum and shipbuilding as subject to stiff new capacity curbs.
Capacity utilization in both steel and cement stood at about 72 percent, the official English-language China Daily reported.
But cutting excess capacity in some sectors may be treating only part of the problem, since the same industries have been behind China's unprecedented urban building boom.
In an NBR policy brief this month, Harvard University professor of political economy (emeritus) Dwight Perkins noted that China had built enough housing in 2011-2012 alone to comfortably accommodate over 100 million people.
Perkins called the pace of construction "not sustainable."
In an interview, Perkins said most of the housing was far too costly for new entrants to China's cities.
"The housing that's been built in the last few years, for the most part, is not available to migrants," said Perkins.
"It's too expensive if it's commercial, and if it's subsidized, it's mainly designed for urban poor that are registered as urban residents," he said.
The current Five-Year Plan calls for building 36 million units of affordable housing in 2011-2015, including 6.3 million this year, according to the official Xinhua news agency.
But many lower-cost apartments are in isolated locations, while others are badly built. On Nov. 10, The New York Times detailed problems of shoddy construction at one such development for migrants in Huaming township near the northern port city of Tianjin.
The consequences of the building boom lead to at least two contradictions.
The first is that cities may be undercapacity for new migrants but at overcapacity for housing they cannot afford.
The second contradiction is that building more housing with materials from high-polluting industries may make cities larger and more unlivable at the same time.
In a policy document released last week, the government promised to ease controls on farmers settling in towns and small cities. Limits on moves to medium-sized cities will be relaxed "in an orderly manner," it said.
The document urged "reasonable requirements" for obtaining hukou in large cities, but said that population size of "megacities" would be strictly controlled, according to Xinhua.
The limits for larger cities may reflect concern for the environmental consequences that have already occurred.
"What they need to do is to somehow find a way through policy to disconnect the pace of energy consumption from both the rate of growth of the economy and the pace of urbanization," said Herberg.
"It can't go on like this," he said, predicting more air quality emergencies. "You're going to reach a point where people start dropping dead in the streets."
Despite the environmental consequences of more construction, Perkins doubts that urbanization will slow down.
The reason is that rural areas offer few job opportunities, particularly for those between the ages of 18 and 40, who are no longer employed in farming.
"Jobs in the rural areas don't amount to much," said Perkins. "The children of migrants who have already left will also leave for the cities to seek work when they come of age," he said.
Despite some warnings that China is running out of "surplus" labor from the countryside, Perkins believes further mechanization of farming will make many more rural jobs unnecessary.
"There's still way too much labor in agriculture," Perkins said.
If demographics and job pressures continue to drive urbanization, China may need even tougher rules for construction-related industries to keep the environment of growing cities from getting worse.
But attempts to cut steel production capacity are also meeting resistance due to effects on profits and jobs.
In northern Hebei province, for example, plans to eliminate 60 million tons of steel capacity by 2017 will lead to an estimated loss of 200 billion yuan (U.S. $32.8 billion), Xinhua reported.
"Who is going to foot the bill for such enormous a loss and the burdens that may come along?" Professor Guo Bin at Hebei University of Science and Technology was quoted as saying.