Chinese police have detained 1,094 people and rescued 382 infants in a nationwide crackdown on four online baby trafficking rings, state media said on Friday, as criminals prey on citizens yearning to escape strict population curbs.

Child trafficking is widespread in China, where population control rules have bolstered a traditional bias for sons, seen as the support of elderly parents and heirs to the family name, and led to the abortion, killing or abandonment of girls.

About 118 boys are born for every 100 girls in the world's most populous country, against a global average of 103 to 107 boys per 100 girls.

The imbalance has created criminal demand for kidnapped or bought baby boys, as well as baby girls destined to be brides attracting rich dowries in sparsely populated regions.

"Child traffickers have now taken the fight online, using 'unofficial adoption' as a front," state news agency Xinhua quoted an unidentified police official as saying. "They are well-hidden and very deceptive."

The traffickers used websites with names such as "China's Orphan Network" and "Dream Adoption Home", highlighting a trend of online deals that make it harder to hunt down the criminals, Xinhua added.

But it did not say what steps authorities were taking to reunite the rescued babies with their parents.

In a separate article, Xinhua warned parents to guard against kidnappers who could pose as nurses in hospitals or lie in wait outside school gates to bundle unsuspecting children into vans or speed off with them on motorbikes.

Last month a Chinese court handed down a suspended death sentence for a doctor who sold seven newborns to human traffickers in a case that sparked public anger.

Zhang Shuxia, 55, an obstetrician in northwestern Shaanxi province, was found guilty of selling the babies for as much as 21,600 yuan ($3,600) each between 2011 and 2013, the court said.

Last year, China, which has a population of about 1.4 billion, said it would ease family restrictions, letting millions of families have two children, in the country's most significant liberalization of its strict one-child policy in about three decades.