Heavily armed gunmen raided a jail in south-central Nigeria late on Sunday and freed 240 inmates - almost everyone in the prison, authorities said.

The attackers started a gun battle with guards at the medium-security prison at Kabba in Kogi State, southwest of the federal capital Abuja, a spokesman for the Correctional Service said.

He did not give details on any casualties.

A total of 294 inmates were in custody at the time - 224 of them pre-trial detainees and 70 convicted, the prison service said. The jail was established in 2008 with a capacity for 200 inmates, it added.

Suspects can spend years in pre-trial detention in Nigeria. Human rights groups say prisons are often overcrowded and legal procedures inefficient.

Nigeria's Controller-General of Corrections, Haliru Nababa, has taken charge of an investigation into the attack and has ordered all the inmates to be recaptured, the prison service said.

"He appealed to the general public to provide useful intelligence that will assist in recapturing the escapees to security operatives," the spokesman said.

(Reporting by Camillus Eboh, writing by Estelle Shirbon; Editing by Toby Chopra and Andrew Heavens)