A couple gets the birth certificate for their second child on Feb 14, 2014. [Photo/Xinhua]

China will probably introduce an overall two-child policy in one or two years, senior demographers expect, as the top population authority said the government would keep fine-tuning birth rules to ensure a sustainable and balanced population growth.

Yang Wenzhuang, director of the family planning grassroots guidance department under the National Health and Family Planning Commission, said the relaxation of the family planning policy in 2013, which allows couples with one spouse being an only child to have a second child, helped lay a solid foundation for future adjustments to the birth rules.

The number of couples who qualify is about 11 million, with nearly 70 percent of them born after 1980, Yang said.

Largely due to the policy relaxation, China had 16.8 million new births last year, 470,000 more than 2013, statistics from the National Health and Family Planning Commission show. Yang expected a bigger increase this year.

"That helps decision-makers make more precise demographic development forecasts and buys more time for socioeconomic and infrastructure preparation to welcome more babies," Yang said at a news conference on Friday.

However, more adjustments are required to "address a major demographic challenge facing the nation: that problems in the population structure, particularly rapid aging, affect economic growth," he added.