The change to China's decades-old one-child policy is a step toward achieving a more balanced population age demographic, family planning officials and experts said.

As part of a blueprint for economic and social reforms drawn up by the Communist Party of China leadership, couples will be allowed to have two children if one of the parents is an only-child.

"The new policy will help maintain a reasonable labor force and slow the pace of population aging, thus benefiting economic growth," said Wang Pei'an, vice-minister of the National Health and Family Planning Commission, during a seminar with population experts in Beijing on Sunday.

Wang said the new policy will mean less risk of families' losing their only child, and also ease children's worries about supporting their aged parents in the future.

The country is facing a series of population-related problems, Wang said.

China's total fertility rate, which measures the average number of children that are born to a woman over her lifetime, has decreased for more than 20 years.

In 2011, the number of women in their child-bearing years (15 to 49 years old) peaked at 490 million.

"The number will be decreasing from that year, along with the tendency for population growth," Wang said.

"If we continue with the current policy, with the total fertility rate continuing to decrease, the population will quickly decrease after the peak, thus affecting the long-term development of the nation," he said.

Meanwhile, the labor-force population (15 to 59 years old) in 2012 was 937 million, a decrease of 3.45 million from the previous year.

The one-child policy also resulted in an increasingly older population, with the number of people over 60 expected to be one-fourth of the total population in 2030 and one-third of the population in 2050.

The sex ratio at birth was also highly unbalanced, with 121.1 boys born for 100 girls in 2004, and in 2012, 117.7 boys born for 100 girls, the highest ratio in the world.

However, Wang said, the authority's research showed that a two-child policy with no restrictions would also be risky, as it would cause a sharp increase in the number of babies born in a short period and put a great deal of pressure on public resources.

"Meanwhile, allowing couples with either of the parents' being an only-child to have a second child keeps the consistency of the policy and is more acceptable to society," Wang said.

Yuan Xin, a professor in population studies at Nankai University in Tianjin, said the new policy will cap the country's population at 1.45 billion by 2030 and postpone the population peak by four years.

Under the new policy, the country's population will drop to 1.39 billion by 2050, Yuan estimated.

Meanwhile, the new policy will help reduce the proportion of people over 60 in the total population from 24.1 percent to 23.8 percent in 2030, and 34.1 percent to 32.8 percent in 2050.

"The policy will help reduce the number of boys born for every 100 girls, as the only way to ensure a gender balance is by allowing couples to have more children," he said.

Zhai Zhenwu, director of the School of Sociology and Population Studies at Renmin University of China, predicts that the new policy will lead to a short-term rebound in the total fertility rate.

"However, the total fertility rate will stabilize after the initial boost in figures," he said.

China's one-child policy was introduced in 1980 to rein in the surging population by limiting most urban couples to one child. The policy was later relaxed so that if both parents were only-children, they could have a second child. However, the one-child policy has greatly reduced the size of families, from 4.43 people per household in 1982 to 3.1 per household in 2010.

The country currently has 150 million households with only one child.

Statistics from the National Health and Family Planning Commission indicate that China's population of 1.34 billion would be 400 million more were it not for the policy.

Shan Juan and Xinhua contributed to this story.