"It is expected that after the adjustment, the number of births will increase, with more than 20 million births expected in a peak year," said Wang Pei'an, deputy head of the National Health and Family Planning Commission.
In a major change to family-planning legislation, the ruling Communist Party of China (CPC) yesterday announced it was abolishing the controversial three-decades-old one-child policy and permitting all couples to have a second child.
According to the National Bureau of Statistics, the population of China in 2014 was 1.368 billion.
Government approval for a second child will be abolished after the new policy is enacted, Wang was quoted as saying by state-run Xinhua news agency.
Wang said demographic problems, an ageing society and the pressure of elderly relatives on a single child had influenced the Party's decision.
The number of women of child-bearing age has dropped significantly, he said.
Wang, however, stressed, "family planning will remain a basic state policy for the long-term", as China still had a large population, which put strain on economic and social development, and the environment.
First introduced in the late 1970s, the family planning policy aimed at reining in the surging population by limiting most urban couples to one child and most rural couples to two children, if the first child born was a girl.
Yesterday's adjustment came after a previous easing of the one-child policy in November, 2013 which allowed couples to have two children if one of them was an only child.
By the end of September, around 1.76 million had applied to have a second child, while the number of births in 2014 increased by 4,70,000 year on year, statistics from the Commission show.
"The change in birth rate has met our expectations," Wang said.
