Even with a tremendous amount of manpower and funds, the upcoming nationwide census in China will still face challenges getting real population data, demographics officials and experts said.

Chinese vice premier Li Keqiang (3rd L) addresses a conference on the 6th national census in Beijing, China, on July 16, 2010.[Xinhua]

The sixth nationwide census will start in November and finish in June 2012. Over six million census takers and nearly 700 million yuan (US$103 million) from the central government will be put into the census, according to the latest report from Outlook Weekly.

However, increasing concern for privacy protection, as well as a rapidly growing migrant population in cities, will make it difficult to gather accurate information about the population, Gu Yanzhou, deputy director of the Beijing statistic bureau was quoted as saying by the report.

More and more people are unwilling to reveal personal information due to increasing concerns over privacy and safety consciousness, he said.

"Especially in those top-flight communities with many foreigners and famous people, not all the residents will patiently give every detail of their lives to strangers, such as how many bedrooms and bathrooms are in their apartments, which will all be asked during the census," he said.

Another difficulty is for the great number of migrant workers moving into cities in recent years.

By the end of 2009, there were more than 17.5 million permanent residents in Beijing, among which more than 5 million were from other areas, according to official figures released on June.

"As the places where they are registered and where they live are not the same, and since many people cannot always be tracked down, it is hard to do a census for the floating population," Gu said.

Also, unregistered births will make it difficult for the census to offer real population figures, he said.

It is not uncommon to hear stories of parents not registering their babies' births to avoid punishment under China's family planning laws.

Public security departments have tried to dispel people's worries, promising to help register all births without punitive measures.

Duan Chengrong, a demographics professor with Renmin University of China, said the most important goal of the census is to get an accurate picture of the local population for policy makers.

"For instance, based on the census statistics, local government plans the locations of hospitals, schools, and bus and subway stations to satisfy the public needs," he said.

Duan said local residents do not need to worry about the census revealing their personal information, as all the information can be used only for the population census.

"The government should take more efforts to win over people's confidence, such as signing privacy agreements," he said.