Gunmen in the early hours of Monday set the correctional facility in Owerri, the Imo State capital, on fire.
The attackers sacked a military checkpoint and raided the police headquarters on the state before the assault on the prison, multiple witnesses told Realm News.
The gunmen struck the prison and freed an unconfirmed number of inmates and suspects. Heavy gunfire also rang through the area.
Amnesty International said over the weekend that Owerri Correctional Centre had 2,156 inmates against its installed capacity of 548 people.
Pictures shared on the micro-blogging site Twitter showed heavy smokes and fire.
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