Several guards were assaulted by the inmates as the clash erupted at Varanasi district jail at Chowkaghat in the Cantonment police station area here, sources said.
The senior jail official who sustained severe injuries has been taken to hospital.
The prisoners have taken control of a portion of the jail barracks andlocked it from inside, they said.
A large police force has been deployed in and around the prison with efforts on to enter the barracksseized by the inmates.