BEIJING -- Even as more than half of the Chinese population currently lives in cities, China's urbanization drive has not given enough attention to quality or provided equal treatment to migrant workers through the years, according to a green paper issued Saturday.

Small and medium-sized Chinese cities will become the key for promoting a better and faster urbanization process, said the green paper on China's small and medium-sized cities in 2012 released at a development forum in Beijing.

Small and medium-sized cities contributed to 56.22 percent of the country's overall economy last year, with a combined gross domestic product of 26.51 trillion yuan ($4.2 trillion), according to the green paper.

More than half of the Chinese population, or 691 million people, are living in cities, representing an urbanization rate of 51.27 percent.

Nevertheless, the quality of the urbanization process remains low, as it is still difficult for rural residents to become urban residents and enjoy the same public services as their peers living in cities.

"China's current urbanization situation lacks quality and is uncoordinated and not harmonious," said Wei Houkai, who led the team to write the green paper.

"To become urban residents, farmers still face obstacles such as high costs," said Wei, who is also deputy director of the Institute for Urban and Environmental Studies with the Chinese Academy of Social Sciences.

CASS studies show that China will need to relocate more than 200 million people living in rural areas to cities and provide job opportunities and homes for them by 2030 if the urbanization process continues at the current speed of 0.8 to 1 percentage point.

Taking into account those migrant workers who have already left the country's farmlands to seek employment in cities, China will have to turn 400 million to 500 million farmers into urban citizens.

Urbanizing those farmers would cost 40 trillion to 50 trillion yuan, Wei said.

"It's apparent that such a problem can't be resolved by the government alone," he said.

He urged the establishment of a diversified cost-sharing mechanism to ensure that migrant workers can enjoy the same treatment in social security, employment, public services, affordable housing and education as urban residents.