Inmates at Port Phillip Prison will remain in lockdown after the discovery of plans for a violent uprising at the maximum security facility that houses some of Victoria's most dangerous criminals.

An intelligence unit at Port Phillip Prison recently found that inmates were plotting to seize control of the facility by staging a fight and then overpowering guards.

There are more offenders aged 25-34 in Victoria than those aged 15-24. Credit:Paul Jeffers

Corrections Victoria and private security company G4S, which operates Port Phillip Prison, have responded to the threat by extending the lockdown, and relocating several violent inmates to other prisons.

Prisoners at Port Phillip Prison have already been confined to their cells for almost three weeks since a riot at the Metropolitan Remand Centre in Ravenhall caused millions of dollars of damage and injured several inmates.