Urbanization

The shrinking family size has dovetailed with slowing population growth. China's population grew by an annual average of 0.53 percent over the past decade, down from 0.57 percent in the previous 10-year period, NBS data showed.

To shore up the number of newborns, the authorities started to allow all couples to have a second child in 2016, and a third last month.

However, Zhuang from the China Population and Development Research Center said there's no need to overreact to the shrinking family size, as the data are susceptible to a wide range of factors other than the birthrate. Some, such as migration, are signs of greater economic vibrancy.

The latest census data showed about 376 million, or one in every four, people in the Chinese mainland are classified as migrants living outside their native prefecture-level hometown, up 70 percent from a decade ago.

Migrants, a phenomenon that emerged after China embraced market-oriented reforms in 1978, usually move from the less affluent rural regions to more expensive places, seeking better-paid jobs and permanent residency.

For decades, the less-skilled worked at construction sites, manned assembly lines in coastal factories and served dishes in downtown areas, playing their roles in the nation's urbanization and economic growth.

The younger have taken up casual jobs, such as food delivery, car-hailing and other app-based business operations, which underpins the rapid expansion of the gig-economy.

However, the hukou, or household registration system, in many locations still hinders out-of-towners from completely merging into the social structure in their residency area, making it financially unpopular to bring families along.

Xiang Yufang, a tutor in Chongqing, is among many college-educated migrants who have acquired a local hukou to buy homes in their adopted city, even when single.

The 24-year-old, whose hometown is about a four-hour bullet train trip from Chongqing, said many out-of-town graduates that she knew of did the same, giving rise to the so-called one-person families.

"I just think I need a home of my own," she said, adding people of her age no longer treat buying homes as part of preparations for marriage.

Yang, the demographer, said stronger financial standing has allowed many, especially women, to have more say over their marital and childbearing status. "They can decide when to marry, or whether to marry at all."