The attack came as confrontation intensified between Nigerian security forces and adherents of the separatist IPOB movement across the South-East.

A correctional facility and police investigations department in Owerri were set alight by unidentified attackers in an overnight operation on Monday, reports on social media said.

Multimedia and witnesses account on social media said the attackers struck the prison and police department shortly after midnight, freeing a yet-unconfirmed number of inmates and suspects. Heavy gunfire also rang through the area, with an account saying over hundreds of inmates might have escaped.

It was unclear how many prisoners escaped, but Amnesty International said over the weekend that Owerri Correctional Centre had 2,156 inmates as against its installed capacity of 548 people.

The level of destruction and casualty figures were not immediately available, but pictures shared on Twitter showed heavy smokes billowing from what posters said were the scenes of the attack that lasted for more than two hours.

Imo police spokesman Godson Orlando said he was unaware of the violence, hours after reports had spread across social media with residents across different sections of Owerri reporting hearing heavy gunshots and explosions.

“I am just hearing it from you now,” Mr Orlando, a police superintendent, said “I will have to wait until later today to find out what happened.”

A spokesman for the correctional headquarters in Abuja did not immediately return a request seeking comments.

The attack came as confrontation intensified between Nigerian security forces and adherents of the IPOB separatist movement across the South-East. Since January, there have been repeated clashes between Nigerian troops and IPOB elements in Imo, Rivers, Abia and Anambra, with both sides denying responsibility for civilian casualties.

Those behind the violence and their motive could not be ascertained before this report was filed.