"We are still investigating the cause of the deaths. But a power generating set was found in the hall where they slept, so we are not ruling out suffocation through carbon monoxide inhalation," police spokesman Ali Okechukwu said.
The family had gathered in a village in the Isiala-Ngwa district of Abia to pray for one of their own whom they said was being haunted by evil spirits.
Though Nigerians are very religious, many are highly superstitious and hold strong beliefs in voodoo, ghosts and witchcraft. One survivor, Linus Abba, said the victims were attacked by the evil spirits they were trying to exorcise.
"I heard strange noises and noticed that the room where we slept was filled with smoke, that is all I can remember because I fainted," Abba told Reuters. "It was a terrible attack by the forces of darkness that we came to fight."
Generator fumes kill scores of people in Africa's most populous country of 140 million every year.