But bureaucrats don't seem to have received the message, fining a couple in a recent widely publicised case for having a third child against the strict letter of the law.

The move has sparked public outrage as people vent their anger at population control officials who are hungry for revenue and have long persecuted couples for violating the now-scrapped "one-child policy".

The Wangs, the couple at the heart of the recent controversy, were ordered by local authorities in Shandong province to pay a fine known as a "social maintenance fee" of 64,626 yuan ($us9,500) immediately after the birth of their third child in January 2017. After various deadlines came and went, the family's entire bank savings of 22,957 yuan ($A4,768) were frozen last month, with the balance still due.

The situation the couple faces has its roots in decades-old fears that China's population would outstrip its resources, along with the ruling Communist Party's all-consuming fervour to control people's most personal decisions.

Family planning regulations emerged in the 1970s, and in 1980 the notorious "one-child policy" came into effect, mandating often brutal punishments for violators ranging from forced abortions and sterilisations to fines and workplace demotions.

Fast-forward 35 years, and a radical change of course was ordered after leaders realised an ageing population and declining workforce threatened to hamstring the country's future development. In 2016, the one-child policy was officially replaced with a two-child policy and Chinese couples were urged to go forth and multiply - within limits.

But the bump in the birthrate was fleeting. Last month, the National Bureau of Statistics said the number of new births in 2018 fell to 15.23 million in a total population of 1.395 billion - a growth rate of .381 per cent and the lowest increase since 1961, resulting in two million fewer births than in 2017.

China's population is estimated to peak at 1.442 billion in 2029 and then gradually decline, potentially fulfilling the conventional wisdom that China will grow old before it grows rich.

Yet the one-child policy has weighed down China with the additional burden of distorted attitudes toward the family, society and child bearing, where one or no children have become the norm, Yi said.

With economic growth the primary guarantor of continued Communist Party rule, the leadership is concerned. The sputtering economy grew at 6.6 per cent last year, its slowest pace in three decades, fuelling fears over the long-term trend of a shrinking pool of workers paying the pensions and health care costs for a ballooning population of retirees.

Even if legal changes do go through, experience in recent years shows that's no guarantee of more children.

Families complain of the soaring costs of housing, education, health care and safe food, an important consideration given China's frequent scandals over food and drug safety.

And many young Chinese who are enjoying activities such as foreign travel are simply putting off marriage and childbirth indefinitely.

Australian Associated Press