China's top three municipalities of Beijing, Shanghai and Tianjin have become advanced urbanized societies, according to the China Urban Development Report 2012.

The report, released by the Institute of Urban and Environmental Studies at the Chinese Academy of Social Sciences on Tuesday, said the population distribution between rural and urban areas is a key indicator of the urbanization level of a country or region.

If the urbanization ratio of the population is between 51 and 60 percent, then it's a primary urbanized society. A medium urbanized society is between 61 and 75 percent and advanced between 76 and 90 percent.

China's top three municipalities of Beijing, Shanghai and Tianjin have entered this bracket, according to the report.

A ratio above 90 percent indicates a complete urbanized society.

It also says China needs to spend 4 to 5 trillion yuan ($786 billion) to provide social security and public services for 400 to 500 million new urban residents in the next 20 years.