Nigerian police have raided a hospital in the south-eastern city of Aba, rescuing 32 pregnant girls allegedly held by a human-trafficking ring.
Aged between 15 and 17 years, the girls were locked up and used to produce babies, said Abia state's police chief.
These were then allegedly sold for ritual witchcraft purposes or adoption.
But the hospital's owner denied running a "baby farm", saying it was a foundation to help teenagers with unwanted pregnancies.
The UN organisation for the welfare of children, Unicef, estimates that at least 10 children are sold daily across Nigeria, where human-trafficking is ranked the third most common crime after economic fraud and drug-trafficking.
But the BBC's Fidelis Mbah in the southern city of Port Harcourt says it is very rare for traffickers to be caught and prosecuted.
Male babies prized
Abia state Police Commissioner Bala Hassan said four babies, already sold in an alleged human-trafficking deal but not yet collected, were also recovered in the raid on The Cross Foundation hospital.
The National Agency for the Prohibition of Trafficking in Persons (Naptip), the organisation charged with fighting human-trafficking in Nigeria, says their investigations show that babies are sold for up to $6,400 (£3,900) each, depending on the sex of the baby.
Male babies are more prized, our correspondent says.
In some parts of the country, babies killed as part of witchcraft rituals are believed to make the charms more powerful, he says.
Human traffickers also put the children up for illegal adoption.
Poor, unmarried women face tough choices if they get pregnant in Nigeria, often facing exclusion from society, correspondents say.
Natip says desperate teenagers with unplanned pregnancies are sometimes lured to clinics and then forced to turn over their babies.
Some of the girls rescued in Aba told the police that after their new-born babies were sold, they were given $170 by the hospital owner.
The police said the proprietor of The Cross Foundation, Dr Hyacinth Orikara, is likely to face charges of child abuse and human trafficking.
Our correspondent says the buying or selling of babies is illegal in Nigeria and can carry a 14-year jail term.
The police carried out similar raids on such clinics in neighbouring Enugu state in 2008.
Three years ago, a Nigerian woman was jailed in the UK for trying to smuggle a baby into the country in order to get on the list for a council flat.