Nigerian police have rescued 13 people, including a child and six pregnant women, from an illegal clinic in southwestern Ogun state, a spokesman said Friday.

The women, aged between 20 and 25, told police the owner hired men to impregnate them and then sell the newborns for profit in what has been dubbed a "baby factory".

The "factories" are usually small illegal facilities parading as private medical clinics that house pregnant women and offer their babies for sale. 

In some cases, young women have been held against their will and raped before their babies are sold on the black market. 

"The operation was carried out on February 28 after an inmate of the home located around Mowe escaped and tipped off the police," police spokesman Abimbola Oyeyemi told AFP.

"We also arrested the owner of the home and two men who are suspected of being hired to impregnate the women," he said.

Oyeyemi said the women told the police that the home's owner usually hired men to sleep with them to make babies.

"They told us that the babies would then be taken from them and sold to patrons," he said.

"The suspects are in custody and they will be charged to court at the end of our investigation," he said.

Police raids on illegal maternity units have been relatively common in Nigeria, especially in the south.

Security services say other cases have seen women with unplanned pregnancies pressured into giving birth in the facilities. 

Baby boys are typically sold for 500,000 naira ($1,400, 1,250 euros) while girls fetch 300,000 naira, police have said in previous cases. 

Last week, 24 babies and four pregnant mothers were rescued in the southern city of Port Harcourt.