The Economist :

Two flaws in the Chinese model of urbanisation are causing these strains. The first is economic. Farmers in China have no property rights, so officials are able to grab agricultural land on the peripheries of urban areas and make money for themselves and their cities by selling it to developers. This is not only unjust; it has also led to a relentless pouring of concrete that has given rise to “ghost cities”—half-empty forests of high-rise office and residential buildings that have sprung up around many cities. The vast debts local governments have incurred as a result of this over-hasty development are the focus of foreign worries about the country’s economic stability.
 This urban sprawl is also exacerbating China’s environmental problems. People need cars to get around the country’s American-style cities. Beijing now has more cars than Houston, as well as some of the dirtiest air on the planet. And it is not just affecting the Chinese. The nation passed America in 2006 as the biggest emitter of carbon dioxide from energy, and is now pumping out nearly twice America’s level.
 The second flaw in the urbanisation model is a social one. China’s cities are now largely made up of two classes, each with a population roughly the size of America’s: a property-owning middle class which enjoys new social freedoms (see article), takes holidays in Europe (see article) and spends like its Western counterparts; and a migrant underclass which toils in factories and menial jobs but is denied public services because its hukou (household registration) is still in the countryside. Both groups have fared well in the boom years; but discontent is growing (see article), and they distrust each other, as well as the party.