China started its once-a-decade census on November 1, with 6 million census takers going door-to-door in 10 days to document demographic changes in the world's most populous country.

Census takers are expected to visit every household and not leave one person uncounted, Feng Nailin, chief of the Population Department with the National Bureau of Statistics, said.

Most people surveyed will be asked to fill out an 18-item questionnaire. Questions to be answered range from residency and children to employment.

Foreigners in China will be surveyed for the first time in the census. But those on a short-term business or sight-seeing trip will not be questioned.