"They blew up the thing with dynamite," national police spokesman Emmanuel Ojukwu told AFP of the attack which took place late yesterday. "Up to 50 inmates escaped," he said, but added that some have been re-arrested.
Local media have reported much higher figures for the number of prisoners freed.
The Koton Karfi prison in Kogi is thought to hold many suspected Boko Haram fighters, but Ojukwu said the raid was not linked to the five-year Islamist uprising, blaming it instead on "criminal activity."
A former spokesman for the insurgent group known as Abul Qaqa, whom the has military claimed to have killed, said at the time that the raid was aimed at freeing several of its members.
Kogi state governor Idris Wada toured the site on Monday to assess the damage, his spokesman Jacob Edi told AFP.