BEIJING, Nov 20 (Reuters) China has vowed fresh efforts to strengthen rural family planning, warning that measures to control population growth in the vast countryside face ''unprecedented challenges''.
With the world's biggest population straining scarce resources, China has enforced rules to restrict family size since the 1970s.
Rules vary but usually limit families to one or, in the countryside, two children.
China credits the sweeping campaign to cajole or force couples to avoid ''excess births'' with keeping its population down to about 1.3 billion and helping to maximise the benefits of economic growth.
But in tens of thousands of villages those policies were strained by growing mobility, lack of a social security net and ''traditional'' ideas about family size, the National Population and Family Planning Commission warned, according to the Xinhua news agency.
Mobile families can avoid official checks, and those with money can pay fines or bribes to have more children.
''At present, rural population and family planning work face unprecedented challenges,'' the commission and over a dozen other agencies warned in a document that called rural family planning ''the number one tough task under heaven''.
''Stabilising low birth rates in the countryside is an extremely arduous task.'' In past years, China has been seeking to soften its draconian and often controversial family control policies, including forced abortions.
But local officials remain under intense pressure to keep numbers down -- leading to skewed statistics, corruption and sometimes brutality.
In May, thousands of villagers rioted in Guangxi region in the country's south, ransacking government buildings, burning cars and clashing with police, after being fined for breaching the one-child policy.
The document urged officials to use rewards and encouragement to make population controls more ''harmonious''.
Rural families who abided by controls should receive financial benefits promised to them, including support in old age or when a child dies, the document said.
Efforts to spread old-age pensions to the countryside should also focus on families with one child or two daughters, it added.
Tens of millions of rural migrants working in towns and cities needed better access to family planning and medical services, it also said.
The government also promised less top-down control of family planning policies. ''Protect the interests of the public, and implement self-administration, self-servicing, self-education and self-oversight by the public,'' the rules said.
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