China's lawmakers have been debating whether the world's most populous country should amend or even scrap its controversial one-child policy, as experts warn of threats of an aging society and labour scarcity.

About 3,000 delegates from all over the country convened in Beijing on Wednesday (March 5) for a meeting by the country's top legislature, discussing key issues and making plans for the new year -- and the country's one-child policy is also a topic for discussion.

In the late 1970s, due to scarce land, water and energy resources, the government restricted most families to having only one child.

Rules vary and families in the countryside are typically allowed to have a second child if the first is a girl, because of a traditional preference for boys.

But after nearly 30 years of family planning some say that it is time for change.

"In a country like China with such a big population, it was necessary to adopt a family-planning policy at that time, and it did play an active role. According to statistics, the policy has helped preventing about 300 or 400 million births. But through the development of economy and living standards and improvement of welfare system, the one-child policy might need to change as well," said Chen Jianguo, an advisor of the legislature and National People's Congress delegate.

Zhao Baige, vice minister of the National Population and Family Planning Commission, was quoted as saying China could slowly change its one-child policy, and family planning had "become a big issue among decision makers". But later state media cited the commission denied the possibility of change.

Local officials who are in charge of family planning say enforcement is difficult.

"I have faced big problems when carrying out the one-child policy. In many cases, we send tickets and fine those who break the family planning law, but the reality is they can't pay the fine," said Liang Xiaodan, a minority delegate from a remote village in southwestern province of Yunnan.

In recent years, China has sought to soften its draconian and often controversial family control policies, which have included forced abortions and other punitive measures.

But the government has also vowed to slap heavier fines on wealthy citizens who flout family planning laws, in response to the emergence of an upper class willing to pay standard fines to have more children.

Beijing says the policies have prevented several hundred million births. But experts have warned of looming problems from an aging population and a growing gender imbalance stemming from aborted or abandoned baby girls and also an eventual scarcity of labour.

Yi Xianrong, economist at the Chinese Academy of Social Sciences, warns that the result of the one-child policy could have an negative impact on the country's economy and long-term development which is much larger than what people expect.

"Over a short period of time, say in five to ten years, the negative effects are not obvious, but after 30 or 40 years, huge problems will appear. If we wait till that time to realize the problems, it will be too late," said Yi.

Population experts estimate that with a rise in education costs, it will be expensive for couples, especially those who live in cities, to have more children. The birth rate has already dropped to 1.8 children per woman from 5.8 in the 1970s and is already below the replacement rate of 2.1.

Low birth rates will lead to an aging society.

According to official statistics, six workers are supporting one retiree in China, but the number will change to two to one in 30 or 40 years time.

For people who have little confidence on the country's pension system, an aging society could create a burden as well.

"It is not bad to have only one child, but I am afraid that the next generation might have a lot of pressure supporting the elderly," said Jiang Xuelian, mother of a four-year-old boy.