The number of registered births dropped by nearly a third in China last year, in the latest sign that relaxations in the country's strict family planning policy are failing to spark a baby boom.

After decades of a "one-child policy", Beijing changed the rules in 2016 to allow families to have two children as fears grew about China's fast-ageing population and shrinking workforce.

Figures from the Public Security Ministry released on Monday showed that the number of registered births fell to 10.04 million in 2020, a drop of more than 30 percent from the previous year.

It marked the fourth consecutive year that figure has declined.

The gender balance was 52.7 percent boys and 47.3 percent girls, according to the official data.

China introduced the one-child policy in the late 1970s in a dramatic effort to slow rapid population growth, before reversing it in 2016.

But the change has not yet resulted in a baby boom, with empowered Chinese women often delaying or avoiding childbirth and young couples blaming rising costs and insufficient policy support for families.

In November, China started a once-a-decade census, with much of the attention on whether it indicates any population bump from the relaxation of family planning rules.

Demographic experts have estimated it could take 15 years for the two-child policy to have any noticeable effect on population numbers. Chinese retirees, meanwhile, are expected to number 300 million by 2025.

Chinese state media in December quoted civil affairs minister Li Jiheng as saying the country's fertility rate has "dropped dangerously", well below the population replacement rate of 2.1 births per woman.