The last census in 2000 put China's official population at 1.295 billion people [EPA]

China has kicked off its once-a-decade census that will see six million census takers go door-to-door to document the massive demographic changes taking place in the world's most populous country.

The census takers began their whirlwind head count on Monday and will conclude on November 10, with the the main data to be released at the end of April.

A 2000 tally put China's official population at 1.295 billion people.

Al Jazeera's Harry Fawcett, reporting from the capital, Beijing, said that he went on a pre-arranged tour with census takers, and as expected, people were very positive about the process.

"But there are key problems, some brought about by social changes in the last few years.

"People are starting to have ideas about social rights and issues of privacy might come into play. Some are unlikely to tell government questioners too much about their lifestyles."

Population shift

In the 10 years since the last census, there has been an extensive shift in the population base as millions of migrant workers have poured into urban areas from the countryside.

It is the sixth time China has carried out a national census but the first time it will count people where they live and not where their resident certificate, or hukou, is legally registered.

The change will better track the demographic changes and will find the true size of China's giant cities, the populations of which have up to now only been estimates.

Citizens' privacy concerns could be one of the biggest challenges for the census takers.

After years of reforms that have reduced the government's once-pervasive involvement in most people's lives, some Chinese may be reluctant to divulge personal information, harbouring suspicions about what the government plans to do with their details.

Another complicating issue are children born in violation of the country's one-child policy, many of whom are unregistered and therefore have no legal identity. They could number in the millions.

The government has said it would lower or waive the hefty penalty fees required for those children to obtain identity cards, though so far it appears there has not been much response to the limited amnesty.

Source: Al Jazeera and agencies