A Victorian prison officer is facing disciplinary action after working a second job as a security guard in the state's bungled hotel quarantine program.
G4S, which operates Port Phillip Prison, confirmed to AAP on Thursday an employee had done shifts with a security firm in Melbourne.
"In recent days, we have received information relating to an employee who, in early April, undertook secondary employment with a security firm without our knowledge," a spokeswoman said.
"The staff member concluded this contract work in late April. The matter is now the subject of internal disciplinary processes."
No staff or prisoners at Port Phillip Prison have tested positive to COVID-19 to date.
G4S has "rigorous health procedures" across its facilities and operations to prevent the spread of COVID-19.
The revelation about the guard comes after more cases emerged in the Victorian prison system.
Corrections Victoria confirmed on Wednesday a prisoner who was in protective quarantine at the Metropolitan Remand Centre returned a positive result after being tested on Monday.
That case followed a Ravenhall Correctional Centre staff member testing positive, which sent that prison and five others into lockdown.
Hopkins Correctional Centre, Langi Kal Kal, Barwon Prison, Fulham and Loddon prisons are the other facilities.
Another inmate at the Metropolitan Remand Centre also tested positive last Friday.
Meanwhile, an inquiry began on Monday into Victoria's botched coronavirus hotel quarantine program, which has sparked a second wave of infections in the state.
Management of the hotel quarantine program is now being organised by Corrections Victoria and Victoria police.