Thirty-two girls were rescued from a maternity home run by a trafficking ring in the west African country’s southern city, Aba, police said.
There are different reports as to how old the girls were, but police spokesman, Geoffrey Ogbonna, told CNN: "There are about 30 pregnant young ladies; the eldest was 20 years old. Some belong in secondary, even in primary school."
The girls, were allegedly locked up at the Cross Foundation clinic so staff could sell their babies for illegal adoption, use in ritual witchcraft or to traffickers who then sell children into forced labour or prostitution.
"We stormed the premises of the Cross Foundation in Aba following a report that pregnant girls are being made to make babies for the proprietor,” said state police commissioner Bala Hassan.
"We rescued 32 pregnant girls and arrested the proprietor, who is undergoing interrogation over allegations that he normally sells the babies to people who may use them for rituals or other purposes."
Four babies, already sold in an alleged deal but not by then handed over, were also rescued in the raid, added Hassan.
The hospital owner allegedly gave the girls £118 for newborn boys and slightly less for newborn girls after they were sold, police said. But the clinic’s director has denied the babies were sold and said the clinic was a home for young women with unwanted pregnancies and that the babies were put up for legal state adoption.
In Nigeria, poor, unmarried women face tough choices if they get pregnant. Unmarried mothers are snubbed by their communities and abortion is illegal except in rare cases, and illegal abortions are very dangerous.
At least 10 children are sold every day across the country, according to the United Nations which ranks human trafficking is the third most common crime in Nigeria - after financial fraud and drug trafficking. Traffickers are rarely caught.
Babies are sold for up to $6,400 each, depending on the sex, the National Agency for the Prohibition of Trafficking in Persons says. Teenagers with unplanned pregnancies are sometimes lured to clinics and then forced to hand over their babies.
Nigerian police carried out similar raids on baby farm clinics in neighbouring Enugu state in 2008. And a Nigerian woman was jailed in Britain three years ago for trying to smuggle a baby into the country to get on the list for a council flat.