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 Nov. 1 to Nov. 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.

China has gone to great lengths to promote the census this year. In Beijing, giant, colorful banners flying across neighborhood gates have slogans such as: "The census is for the nation and each citizen," and "Everyone participates in the census."

Unlike the U.S. census, where residents are asked to fill out and mail in forms in a yearlong 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 situation, and resident status.

One of the first to be counted Monday in Beijing was retiree Ren Shuanggeng, who flashed a big smile to welcome census takers into his apartment in central Beijing.

Two neighborhood surveyors decked out in census vests with identification badges spared no time in reeling off questions.

"How many years have you lived here? How many people live here? Where do your children live? How old are they? How long have you been retired?"

Ren is one of more than 1.3 billion Chinese whom officials aim to question — a mammoth task considering the almost constant swirl of undocumented migrant workers on the hunt for better jobs.

Every census-taker covers about 80 to 100 households, where about 90 percent have to answer 18 questions about home ownership, jobs and family members, said Cai Jun, an official with the Beijing census committee. The other 10 percent, randomly selected, take an extended 45-question survey that seeks further information on reasons for moving, unemployment and other personal details.

"Going door-to-door allows us to be thorough so that we can survey migrant workers and others who may not have a permanent address in Beijing," said Cai.

This is the first year foreigners, plus people from Hong Kong and Macau, will be counted, said Cai. They will be required to answer only eight questions.

One of the biggest challenges is to document China’s migrant or "floating population," which will show the government 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 whom remain unregistered.

Under China’s hukou household registration system, citizens are designated urban or rural. This means many migrant workers registered in their hometowns are denied access to government services in cities, including health care and education.

Census-takes 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, those 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.

"We will go to factories, remote areas and universities to hold mass events so no one will be missed," Cai said. "It is our goal to cover everyone regardless of the challenges."

Preliminary work began in August with millions of census-takers knocking on doors to get basic information on residents and landlords, including names and telephone numbers.

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, Cai said.

Increased privacy concerns present another hurdle this year. Although Ren was open to the census, citizens have also become less cooperative in sharing personal details as they become increasingly aware of their rights to privacy.

Census-takers are required to signed confidentiality agreements, but after years of reforms that have reduced the government’s once-pervasive involvement in most people’s lives, some Chinese may be reluctant to give up personal information, harboring suspicions about what the government plans to do with their details.

"Some people think asking these personal questions is an invasion of privacy, but I have nothing to hide," said Ren, who moved to Beijing more than 50 years ago from neighboring Hebei province.

The names and sometimes photos of census-takers are posted on neighborhood bulletin boards to help residents avoid scam artists who may pose as census-takers.

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 during the census is to be released at the end of April.

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Associated Press researcher Yu Bing contributed to this report.