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, state media agency Xinhua said.
"Child traffickers have now taken the fight online, using 'unofficial adoption' as a front," an unidentified police official told Xinhua.
"They are well-hidden and very deceptive."
However, it did not say what authorities were doing 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.
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 for every 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.
Last month, a Chinese court handed down a suspended death sentence for a doctor who sold seven newborns to human traffickers.
Zhang Shuxia, an obstetrician in north-western Shaanxi province, was found guilty of selling the babies for as much as $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.
It was the country's most significant liberalisation of its strict one-child policy in about three decades.