Mass kidnappings are a common way for gangs and armed groups to make quick money in Nigeria.

Gunmen have raided an orphanage and kidnapped at least 23 children, authorities in Nigeria report.

The gang took the children late on Sunday from an unregistered facility called the Dahallukitab Group of Schools, located in an “isolated area” in Kogi State’s capital, Lokoja, Kogi Information Commissioner Kingsley Fanwo said in a statement on Monday.

Mass kidnappings have become a common way for gangs and armed groups to make quick money in Africa’s most populous country, especially in rural areas with little government presence.

Fanwo said the “prompt and coordinated response” of security agencies led to the rescue of 15 children but eight are still missing.

The wife of the proprietor of the orphanage was also abducted, according to the statement.

“Intensive operations are ongoing to secure the safe return of the remaining eight victims and apprehend the perpetrators,” the official said.

The orphanage was operating “illegally” in a remote location without the knowledge of relevant authorities and security agencies, Fanwo added.

The statement did not disclose the ages of the abducted children, but it referred to them as “pupils”, which in Nigeria usually refers to someone in kindergarten or primary school, covering ages up to 12.

No group immediately claimed responsibility for the attack.

Nigeria faces multiple conflicts from long-running violence by the Boko Haram armed group to “bandit” gangs, farmer-herder violence and southeastern separatists.

The ISIL (ISIS)-linked Lakurawa group also operates in communities in the northwestern part of the country bordering Niger.

The North Central Zone of Nigeria, where Kogi is located, has seen violent attacks, including raids on schools, in recent months with some of the attacks blamed on armed groups.

Hundreds of students were taken by gunmen from their school in neighbouring Niger State in November in an attack security sources blamed on Boko Haram.