Prisoners were well aware in advance militants would carry out an assault in the central jail in Dera Ismail Khan, and geared up for escape immediately after hearing the first gunshot.
Reports suggest that the attackers stayed for over three hours inside the jail before attempting escape.
According to the Express Tribune, armed with guns, mortars, rocket-propelled grenades and bombs, the militants bombarded the prison before fleeing with their accomplices.
As the militants were attacking the jail, the officials sought refuge in underground 'nullahs', despite being given a precautionary security drill a day before.
An official of the district police said that around 248 prisoners escaped from the jail, including 49 high-profile militants, six death row prisoners and five females, the report added.