The attackers reportedly entered the prison yard in the south-eastern town of Owerri by using explosives to blast the administrative block.
Six prisoners have reportedly returned, while 35 refused to escape.
Police have accused the banned separatist group, the Indigenous People of Biafra, of carrying out the attack. It has reportedly denied involvement.
The Nigerian Correctional Service has confirmed that 1,844 inmates escaped from the jail in Imo state.
