The policy change is currently being deliberated by the country's top Legislature.
The one-child policy was introduced in 1979 to control the country's population, limiting most couples, especially in urban areas, to just one child. Last month, the Communist Party of China decided to relax the rules by allowing couples to have a second child if one of the parents is an only child. Previously, a husband and wife were both required to be single children if they wanted a second child.
The Chinese Cabinet submitted a bill altering the policy to the Standing Committee of the National People's Congress, which began meeting this week.
Zhai Zhenwu, director of population studies at Renmin University of China, told China Daily the policy change would lead to a mini baby boom lasting five or six years, with an additional 2 million births a year on average. He is among experts appointed by China's National Health and Family Planning Commission to assess the largest possible population growth under the new policy.
Zhai said the new policy would make as many as 20 million Chinese couples eligible to have a second child. He said a survey he conducted a year ago showed more than 60 percent of newly eligible families were willing to have a second baby.
During the baby boom, he said a peak of about 3 million new births could be expected in the third year and that the additional births would eventually settle at 1.6 million each year with little fluctuation.
"If China continues the old policy, the birth rate would continue falling and lead to a sharp drop of the population after reaching a peak," Li Bin, minister of the National Health and Family Planning Commission, told the Standing Committee.
The report said the country's working population began to drop in 2012 by 3.45 million annually, and it is likely to fall by 8 million annually after 2023. Those aged 60 and above will reach 400 million and account for a quarter of the population by early 2030s, up from a seventh now.
"It is the right time to do it as the low birth rate is stable, the working population is still large and the burden to support the elderly is relatively light," Li said.
The new policy is expected to take effect early next year.