OWERRI: Tension gripped a town in southeastern Nigeria on Tuesday, a day after gunmen blasted their way into a prison, freed more than 1,800 inmates and then looted a police station, local inhabitants said.

The town of Owerri was calm but the mood was apprehensive, as residents said they worried about violence from escapees or being caught in an attack by the security forces.

"Many are afraid that the escapees may return... while others are thinking that the security forces will come for a reprisal," said local journalist Damian Duruiheoma.

Security in the area was heavy, he said.

"The areas attacked have been cordoned off," he said.

Gunmen using explosives and rockets blasted their way into Owerri prison at dawn on Monday, engaging guards in a gun battle and breaking out inmates, the Nigerian Correctional Service said.

A total of 1,844 inmates were freed.

A senior prison official told AFP that some of the prisoners had returned and a hunt was underway for the others.

Local media said the state police's main office in the town was also raided by the attackers, who looted its armoury and torched dozens of vehicles.

Resident Chizoba Ekeh told AFP that "everyone is being careful while going about their normal businesses."

Another inhabitant, George Onyemuwa, shared this concern.

"A situation where police and military equipment were destroyed and you are asking if there's apprehension?" he asked rhetorically.

"People think that there may be reprisals," he said.

"We do not know who the perpetrators are but I think the government needs to do something before it gets out of hand," he added.

No group has so far claimed responsibility, although President Muhammadu Buhari called the attack an "act of terrorism" carried out by "anarchists" and urged security forces to capture the assailants and the escaped detainees.

Prisons in Africa's most populous country are often overcrowded.

As many as 70 percent of inmates are on remand and can be held awaiting trial for years.

Imo state is part of a region that has long been a hotbed for Nigerian separatist groups and where tensions between federal authorities and the indigenous Igbo population are often high.

The Indigenous People of Biafra (IPOB) separatist movement has recently been posting videos on social media of dozens of its militiamen in training.

But IPOB spokesman Emmanuel Powerful rejected any involvement in the prison break, sending a statement to AFP that dismissed such accusations as "lies".

Calls for a separate state of Biafra in the south are a sensitive subject in Nigeria, after a unilateral declaration of independence in 1967 sparked a brutal 30-month civil war.