China is about to embark on its sixth national census - the first in 10 years.
More than six million workers have been hired for the task.
The BBC reports authorities hope it will clarify the number of migrant workers in the country, which by some estimates is more than 200 million.
Earlier this year, Premier Wen Jiabao said migrant workers need better treatment.
Tens of millions of Chinese have moved from the countryside to the cities in search of work in recent years.
It is also hoped that the census will reveal how many children there are in China, which is generally under-reported.
China's population is more than 1.3 billion.