The arrangement, not widely reported, took effect at least one year ago, according to Wang Xu, also director of the commission's Science and Technology Institute.

"It indicates the government has been fine-tuning the State policy on family planning," he told China Daily.

The legislator said it is the right time to further optimize the policy.

The number of people aged between 19 and 59 declined by 3.45 million year-on-year in 2012 on the Chinese mainland, making a significant dent in China's labor force.

The number of people aged 60 and older is estimated to top 200 million in 2013, according to a report on the aging population released by the Chinese Academy of Social Sciences on Feb 26.

There are changes in the size, structure and geographical distribution of the country's population, so the policy should improve to match the changes, the lawmaker said.

Had the country's family planning policy not been in place, China's population would be at least 400 million larger, he said. Given the sheer size of the current population, China should continue to stick to the basic family planning policy and stabilize the low birthrate, he added.

"We may consider extending the second-child policy now in place in the rural parts of seven regions including Shanghai and Tianjin to urban regions as well," he suggested.

Liu Dajun, a political adviser, agreed with Wang. The member of the National Committee of the Chinese People's Political Consultative Conference said China's population will start to decline in 2030 under the current policy.

"We have missed the best time to roll out the policy of allowing one couple to have two children. For the future of our country, we call for immediate action in adjusting the family planning policy," Liu said in a proposal submitted to the national committee.