GUIYANG - City mayors across China are struggling to find answers for one problem -- how to balance environmental protection and urbanization.

At an international environmental protection forum held in Guiyang, capital of Southwest China's Guizhou province, mayors and other senior city officials took part in a heated debate about sustainable development in their cities.

"We are not worrying about the expansion and development of our cities, but the speed of expansion, which may be a bit too fast and may not be sustainable," said Yao Yingjie, deputy mayor of Changsha, capital of Central China's Hunan province, which has boomed thanks to economic development in the region.

Yao said the city's population is expected to grow by 200,000 to 300,000 people annually, which will place great pressure on the city's facilities and environment.

The Changsha government is trying to improve public services and infrastructure in its suburban townships so that people will be more willing to stay there instead of moving to downtown areas.

The city has also held special training programs for new township officials to raise their awareness of the importance of environmental protection.

For the city of Zaozhuang in East China's Shandong province, the government is facing the tough task of transforming the city, which has traditionally been dominated by the coal mining industry.

"Coal mine reserves in Zaozhuang may only last 15 to 20 years. Where the city will go is an urgent question," said Zhang Shuping, mayor of Zaozhuang.

The city has closed about 30 outdated coal mines last year to improve the efficiency of the industry and protect its resources. Greening programs have also been used to remedy the damage done by the coal industry.

The city is also introducing new industries and encouraging locals to take up jobs in sectors outside of the coal industry.

"These transformation projects have damped our economic growth figures but the city is moving toward a promising future," Zhang said.

About 52 percent of the Chinese population lived in urban areas last year, up 20 percent from the early 1980s, representing an urbanization growth rate that is much faster than that of developed countries.

Earlier this week, national political advisors held a special meeting to discuss problems and risks related to rapid urbanization.