China will loosen its famously strict family planning policy on a trial basis in five provinces next year to allow more couples to have a second child, a demographer says.

The change - allowing couples to have two children if one of the spouses is an only child - will be enacted in Heilongjiang, Jilin, Liaoning, Jiangsu and Zhejiang, provinces with low birth rates, said He Yafu, an independent demographer quoting sources among policymakers.

Meant to counter the trends of a graying population and a shrinking workforce, the plan will eventually expand to all of China's provinces, He told reporters of the Outlook Weekly.

It could mark a remarkable revision of the nation's family planning limits that prevented 400 million additional births over three decades.

But officials from the National Population and Family Planning Commission said a nationwide relaxation is not coming soon.

They said China is sticking to its current policy, which restricts most urban couples to have one child and rural couples to two. An extra child can cost a couple a penalty of up to 100,000 yuan (US$ 14,985).

Officials of all five designated provinces said they had received no notice from higher-level authorities despite the widespread rumors and growing speculation.

The strict family planning rule has largely controlled the country's population, projected to peak at 1.65 billion in 2033, but also has brought a variety of problems, including one of demographic imbalance: As the nation's older people grow more numerous, the cohort of youngsters for the labor force that would support them has been getting smaller.

China's over-60 population reached 167 million, or 12.5 percent of total population, last year.

It will top 200 million in 2015. Meanwhile, China's working population, now 19 percent of the total, is projected to fall by 10 million per year after 2025.

It adds up to bad news for the social welfare system.

Critics also blame the one-child policy for a skewed gender ratio - 119 males for every 100 females - because of some Chinese families' traditional preference for boys.

By 2020, the imbalance could lead 24 million marriageable Chinese men to be wifeless, said a report by the Chinese Academy of Social Sciences.