A few places in China give parents a rare right to have two offspring rather than one, but many stop at a single child anyway -- fuelling demands to end what critics call an unnecessary, harmful rule.

"If you have too many kids then it becomes difficult," said Lu Xiuyan, a 42-year-old restaurant manager in Jiashan, a dusty village of low-slung buildings a few hours north-east of Beijing, who has one son.

"But if you have fewer kids, you have less of a burden and you'll be a little better off."

The national one-child policy was imposed more than 30 years ago, with enforcers relying on permits, fines and sometimes late-term abortions. Opponents say it has led to widespread rights abuses and major demographic imbalances.

Self-imposed birth limits in places such as Chengde district, which includes Jiashan, show the policy is not even required for population control, they say.

China's family planning commission, whose hundreds of thousands of personnel ensure the rules are followed, was merged with the health ministry at the country's annual parliament meeting earlier this month.

The move also saw population policymaking handed to a body overseeing economic growth, giving critics faint hope that change might be in the works.

It marked a "step in the right direction," said Peking University population expert Li Jianxin.

"Any way you look at it the policy should be cancelled, based on rights, based on the consequences on the ground."

China says avoiding overpopulation has helped speed the nation's rapid economic development.

But with a shrinking labour pool that could weaken growth and a swelling elderly population that will require care, Li and others argue that China should worry more about boosting the number of births.

Its estimated fertility rate of 1.5 children per mother is well below the "replacement" level of 2.1.

Even if the policy were immediately abolished, births might rise 25 percent for a few years but then drop back to near current levels, said Wang Feng, director of the Brookings-Tsinghua Centre for Public Policy in Beijing.

Already numerous exceptions, often set at the local level, mean that in practice only 60 percent of Chinese are limited to one child.

Ethnic minorities and couples who are both only children can often have more than one.

Many rural areas allow families whose first child is a girl to have a second, and Chengde is one of a scattering of areas running a two-child policy regardless of gender.

But surveys around China have shown that for many parents, having more than one child has grown too expensive as housing, education and other costs have spiralled.

A fall in China's fertility rate would be consistent with global trends as people grow wealthier and move to cities.

"There is a very strong correlation between urbanisation, economic development and fertility decline," said Cai Yong, a professor at the University of North Carolina at Chapel Hill.

"Chinese people are right now so concerned about economic gains that for many of them having a child is a very costly thing," he said. "There should not be any concerns in relaxing this policy."

A 2006 study of families in Chengde found that about half had opted to have two children while 40 percent stuck to one.

Less than four percent of people said they wanted three or more children, while 70 percent said two was ideal, mostly to prevent loneliness, and 25 percent said one was best, mainly for better quality of life or education.

Zhu Chenghui, a 60-year-old retiree in Chengde fetching his seven-year-old grandson from school, said he had tried to convince the boy's parents to have a second.

"One, they think it's inconvenient, and two, they think it's a burden," he said. "Nowadays a lot of people are allowed to have two, but in their minds it's not important."

Shopkeeper Hu Fengzhi, 46, found having two children helpful because the elder could look after the younger.

One of seven siblings herself, she said that if no restrictions existed she might have borne another two -- a minority view, but one that policymakers fear.

While experts maintain China can safely abolish the policy immediately, the authorities have dismissed talk of change.

"After the reform, China will adhere to and improve the family planning policy," senior cabinet member Ma Kai said earlier this month as he announced the government restructuring.

Nonetheless several experts expressed cautious hope that the reshuffle signalled an intent to rethink the policy, or would at least disrupt family planning enforcers' operations.

"Of course we hope that the current policy can be cancelled as soon as possible," said Li of Peking University. "The sooner the better."