Childless families have now become the mainstream in Hong Kong as the city's fertility rate continues to plunge, according to the Family Planning Association.

The group polled 1,502 married or cohabiting women and many of their partners between September and December last year, and found that the number of childless women have more than doubled from five years ago to 43.2 percent last year.

The average number of children per woman, meanwhile, plummeted from 1.3 in 2017 to just 0.9 last year.

The chairman of the association’s research sub-committee, Paul Yip, attributed the SAR's low fertility rate to people marrying late.

"Because of the delay in the marriage itself, the window for conception becomes smaller," Yip said.

He said while small families are common in high-income societies, the government should do more to encourage childbirth.

"It’s time that we have a rethink of how the whole society can work together, create a friendlier working environment, and then create a more conducive environment for people who would like to stay in Hong Kong to give birth in Hong Kong," he said.

The population expert said financial incentives and the provision of more childcare services may encourage couples to have more babies.