Firefighters called to a blaze inside a Melbourne jail say they have been confronted by the chaotic scene of prisoners, who should have been locked down, wandering about the burning prison wing.

Eight prisoners and one prison officer suffered injuries ranging from smoke inhalation to burnt windpipes from the fire inside the Charlotte wing of the Port Phillip Prison at Truganina about 10pm (AEST) on Saturday.

"Normally when we go into a fire scene prisoners are locked down," Metropolitan Fire Brigade Commander Frank Besanko said.

"There was a pretty intense fire going with limited numbers of staff trying to evacuate 33 prisoners."

Police are investigating the blaze which caused $80,000 damage.