A blue book released on December 14 showed that Beijing's permanent population has continuously dropped in two recent years while getting much older. Meanwhile, the capital's subcenter, Tongzhou District, has seen more population growth since Beijing has been shifting noncapital functions to neighboring areas.

In addition, the blue book, issued by the Beijing Population and Social Development Research Center and the Social Sciences Academic Press, finds that the capital's migrant population has been declining since 2015. In 2018, it had fallen to 7.65 million, down 3.74 percent year on year.

Experts say that as Beijing's noncapital functions are gradually moved out, and with the crackdown on illegal structures, migrants have faced more pressure living and working in Beijing, causing a continuous decline in their population.

Beijing's permanent resident population - people with hukou, or those without who have lived in the city for more than six months - also shrank in the past two years. In 2018, the permanent resident population was 21.5 million, 165,000 fewer than in 2017, according to the report.

Yang Hongshan, a professor at Renmin University of China's School of Public Administration and Policy, said municipal authorities' campaign to demolish illegal buildings has raised the cost of living for migrants, making it harder to find housing.

"Their work opportunities were also reduced by the municipal government strengthening curbs on environmental pollution and the relocation of many factories," he said.

Meanwhile, the capital has been moving administrative departments to Tongzhou District, which has thinned the population density of downtown Beijing, he added.

In 2018, the number of permanent residents of Tongzhou reached to 1.58 million, 70,000 more than in 2017, the report said. Tongzhou's migrant population was 657,000, which is 98,000 more than in 2015.

"It will still take some time for Tongzhou to fully be able to accommodate more people, as supporting facilities for government agencies and other public facilities, like hospitals and schools, are gradually being built," said Yang.

The report also showed that the aging of the Beijing population accelerated significantly in 2018, compared with the juvenile population of newborns to 14-year-olds. The juvenile population, made up 10.52 percent of the total last year, while people age 65 and older, accounted for 11.21 percent.

Dang Junwu, deputy director of the China Research Center on Aging, said Beijing has in recent years become a hyperaging society, one that has a significant proportion of people age 80 or older.

"The aging population is a normal social transformation and part of the reason is due to low fertility in big cities," he said, explaining that college educated women prefer to delay having children as they engage in other pursuits.

The report also suggested how to formulate public service policies needed to adjust to the current demographic for the aging society.

Since 2010, the education level of Beijing residents has improved. In 2018, nearly 40 percent had a college undergraduate education or higher, according to the report.

Beijing has long planned to cap its population at 23 million by 2020 and maintain that level for the long term.