BEIJING -- A week after releasing its 2020 census, China has begun revising demographic data for most of the preceding decade upward, raising concerns about the integrity of its statistics in the face of a looming population decline.

The government is adjusting the birth data for 2011 to 2019, which was based on a sample of about 0.1% of the total population. This comes on the heels of suspicion over how the 2020 head count of children greatly exceeded the total number of babies reported born in the years prior.

The National Bureau of Statistics is working to revise such numbers as the total population, births and the urbanization rate for 2011 to 2019, spokesperson Fu Linghui told a news conference Monday. The number of births will go up by about 1 million per year on average, he said -- the equivalent of a 6% increase for the entire nine-year period.

For example, 2016 births will be revised to 18.83 million and 2017 births to 17.65 million, up 970,000 and 420,000 from the previously announced figures, Fu said.

China samples about 0.1% of its population to track demographic data every year, except for when a door-to-door census is conducted once a decade, and in the fifth year between two censuses, when over 1% of the population is surveyed.

Sample surveys have inherent limitations, like potentially overestimating or underestimating certain data. But it would be highly unlikely for birth numbers from nine separate years to all require an upward correction.

Fu said the bureau is making adjustments in accordance with international practice. But doubts have been cast over this claim. Japan makes no such revisions, a census official there said.

Beijing is believed to be rushing for updates to narrow the glaring data gap that emerged after the release of its census.

That count showed the country with 253.38 million children 14 and younger in 2020. But new births between 2006 and 2020 -- the period during which they would have been born -- totaled about 239 million based on data that includes the sampling survey results, resulting in a significant discrepancy of over 14 million.

Chinese authorities dismiss allegations of padding the census results.

With the population seen on the verge of officially shrinking, the Chinese data has come under greater scrutiny.

"Chinese demographers said that although China reported population growth in 2020, the general declining trend was inevitable, and China's population is likely to start to decline as early as 2022," reports the Global Times, a newspaper affiliated with the ruling Communist Party.

Yi Fuxian, a scientist at the University of Wisconsin-Madison in the U.S., believes that the population already decreased in 2020.

With its 2016 move to allow all married couples to bear children twice instead of just once, the Communist Party leadership is eager to show that the new two-child policy is working. There is speculation that the data revisions are driven partly by a desire to deflect criticism of the long-running family planning program.