A forest of buildings and cranes rises through thick fog above roads jammed with cars in a Chinese city the size of Austria and home to more than 32 million people.
The southwestern megacity of Chongqing is bursting at the seams as authorities struggle to keep pace with its rapidly growing urban population -- a situation seen repeatedly across the vast country of 1.3 billion people.
Lifelong resident Zhou Dechong, 80, says he is stunned by the speed of development in the teeming metropolis which, like many Chinese cities, is plagued by chronic traffic jams, dirty air and the deafening sound of jack-hammers.
"In every aspect, the pace of development has been very fast," Zhou told AFP.
More than 350 million people are expected to move to Chinese towns and cities in the coming years, boosting the country's urban population to one billion by 2030, according to a report by consultancy firm McKinsey & Company.
The unprecedented urbanisation will more than double the number of cities with one million residents to 221 and require the construction of five million buildings, including 50,000 skyscrapers -- equivalent to 10 New Yorks, it said.
The staggering expansion is putting enormous strain on China's already depleted natural resources and could trigger more social unrest as millions of people leave the countryside to live in densely populated urban areas.
"There's going to be more volatility and uncertainty," Jonathan Woetzel, a Shanghai-based director for McKinsey, told AFP.
"Urbanisation essentially picks you up and moves you to a place where you don't know anybody nor do you have as many formal rights as you would have had in your previous residence."
It means living "cheek by jowl with other people who they have never met and literally don't share a common language with nor do they have the same sense of rights and responsibilities," Woetzel said.
University of Sydney professor Lu Duanfang said the massive human migration would also have "huge ecological implications" as valuable farmland near urban areas is used for high-rise buildings, and demand for energy and water soars.
"As more peasants convert to the modern urban living style, it will cost more energy" as more people use microwaves and washing machines, said Lu -- a specialist in architecture, design and planning.
Land sales -- a key source of revenue for cash-strapped local governments -- also threaten China's food security by reducing the area available for growing crops and grazing animals needed to feed the world's most populous country.
Demand for resources is likely to double while air pollution -- already severe in many cities -- could reach "critical levels" without further investment in green technology, the McKinsey report said.
The burgeoning urban population has sparked a nationwide building boom as China spends billions of dollars developing new cities, power plants, roads, high-speed rail networks and airports to accommodate the masses.
Authorities -- anxious about the widening wealth gap -- have pledged to reform the controversial household registration system so migrants can access public services such as health insurance and free education when they relocate.
After 30 years of rapid growth, Chinese cities such as Beijing and Shanghai are starting to groan under the strain of populations the size of Australia's at more than 20 million.
Officials are trying to relieve the pressure by restricting the number of cars allowed on the roads and urging people and companies to move inland.
But analysts say the key to successful urbanisation will be maintaining the country's rapid economic growth -- a blistering 9.7 percent in the first quarter -- so enough jobs can be created for the new urban dwellers.
"China is very much an expectations-driven environment -- as long as people feel like it is getting better, then the base for fundamental social stability is there," said Woetzel.
"If you are out of work for a long period, one loses the expectation of things getting better."
Lu agreed, saying, "As long as the growth rate is high, it doesn't matter how many are moving into the cities. Density itself is not a problem; what matters is whether the economy can sustain itself."
So far, the government has done "pretty well" moving more than 300 million people into urban areas in the past three decades, said Paul Kriss, a World Bank urban specialist based in Beijing.
"You don't see the major slums like you see in India, Cairo or Lagos or in South America," Kriss told AFP. "Having said that, they do have mega-challenges."