BEIJING -- More Chinese cities may restrict vehicle purchases in a bid to fight air pollution and traffic congestion, state media reported.

With more than 13 million cars sold in China last year, motor vehicles and their emissions have emerged as the chief culprit for the air pollution in large cities.

Beijing, Shanghai and two other cities already curb the purchase of vehicles for private use, through lotteries and auctions of a limited number of license plates.

Shi Jianhua, the deputy secretary general of the government-backed China Association of Automobile Manufacturers, was quoted Thursday as saying that eight more cities are likely to announce similar policies. The eight include the port city Tianjin, near Beijing, the metropolis Chongqing in the southwest and industrial powerhouse Shenzhen, not far from Hong Kong.

Such restrictions might cut vehicle sales by 400,000 units, or 2 percent of total domestic sales, and have a "certain impact" on the country's economic growth, the China Daily newspaper quoted Shi as saying.

The automakers' group, which consults with local governments and makes recommendations on vehicle policies, declined to offer details when called.

China's increasingly informed and vocal citizens have successfully pushed the government to be more transparent about how bad the air in their cities is, but, as they get richer, their desire for cleaner air conflicts with their growing dependence on cars. While China is the biggest car market in the world by number of vehicles sold, there is still plenty of room for growth as the country still lags far behind developed markets in terms of the ratio of cars to people.

The number of vehicles in Beijing has increased to 5.18 million from 3.13 million in early 2008, Xinhua reported earlier this year. Since the beginning of last year, prospective buyers have had to enter a monthly draw to win a license plate. Each month, 20,000 lucky winners are chosen. The number of people in the draw had reached almost 1.53 million by last month.

Zhao Jian, a transport expert at Beijing's Jiaotong University's School of Economics and Management, said extending restriction-on-ownership policies to other cities was unlikely to have much effect on pollution because there were already too many cars on the roads.

"The restrictions on car ownership in Beijing failed to achieve what the government wanted to see because the restrictions only slowed the growth in the number of cars. They didn't reduce the numbers of cars," Zhao said.

"Even with proper enforcement, the policy still won't solve the air pollution problem, neither will similar measures in other cities," Zhao said.

Vehicle emissions are compounded by a lack of effective public transportation, low emission standards and the slow development of energy-saving and clean automobile technologies, the Asian Development Bank said in its 2012 environmental analysis of China.