China kicked off a once-a-decade census Monday, a whirlwind 10-day head count that sees 6 million census-takers scrutinize apartment blocks, scour migrant areas and scan rural villages to document massive demographic changes in the world's most populous country.

And they aim to count every person.

The 2000 tally put China's official population at 1.295 billion people, but missed migrant workers living in cities for less than six months. In the 10 years since, there has been an extensive shift in the population base as tens of millions of migrant workers have poured into urban areas looking for work.

"Wherever you are living from November 1 to 10, you will be counted," said Zhang Xueyuan, director of the publicity for the Beijing census committee.

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 find the true size of China's giant cities, the populations of which up to now have been only estimates.

Unlike the US census, where residents are asked to fill out and mail in forms in a year-long undertaking, Chinese census-takers plan to speed up the process by going door-to-door asking people questions about their education level, family history, employment and resident status.

Every census-taker covers 80 to 100 households, where about 90 percent have to answer 18 questions about home ownership, jobs and family members.

The other 10 percent, randomly selected, take an extended 45-question survey that seeks further information on reasons for moving, unemployment and other details.

One of the biggest challenges is to document China's migrant or "floating population," which will provide a better picture of the numbers in its giant cities. About 140 million migrant workers work outside of their hometowns, according to a 2009 National Bureau of Statistics report. Many of these remain unregistered.

Census-takers could face difficulties getting migrant workers to share personal information if they are working in cities illegally or have given birth while residing in a city without proper documents.

Families with unregistered children may also be reluctant to provide information. China has a one-child policy and parents with children born in violation of the rule are required to pay a hefty fine. To encourage people to come forward, penalties will be reduced for families if they register their extra children in the census.

This year, census-takers vow to reach everyone.

Census takers are expected to visit universities, factories and construction sites where migrant workers are living in temporary housing - with the goal of surveying millions of people who have migrated into China's urban centers and are often unaccounted for.

Most of the 6 million census workers are employees of local district governments or members of neighborhood committees, which often consist of retired government employees.

There have been no published predictions on how much China's population has grown in the last decade, but if it grew by just 1 percent a year, that would be an addition of 130 million people - or nearly half the population of the United States - in just 10 years.

The main data gathered will be released at the end of next April.

(Shanghai Daily November 2, 2010)