A group of about 10 staff posed as patients in the waiting room of Colac Area Health's Urgent Care Centre in August 2023, a Victorian Health Department probe found.
The full report has not been made public but the executive summary states there was a "real possibility" that patient care could have been impacted.
It also found arrangements were made for at least one ambulance to arrive at the clinic with a person who did not require medical treatment and a staff member who didn't need treatment was on a trolley in a corridor.
"Each of those actions were taken in order to make it appear to the minister that the (clinic) was busier than it actually was on the day of the visit," the summary said.
Mary-Anne Thomas says she had no cause to think anything was amiss. (Diego Fedele/AAP PHOTOS)
The fake patients were registered in the clinic's records before the minister arrived and were then removed after she left.
Health Minister Mary-Anne Thomas said she was disappointed by what happened and didn't notice the ruse.
"I had no reason to think that anything was untoward," Ms Thomas told reporters on Wednesday.
"It's certainly not something that ever crossed my mind."Â
The minister does not believe any similar incidents have happened at other health facilities.
"Our health service is full of dedicated, hardworking, committed doctors, nurses and allied health teams," she said.
"This type of behaviour is completely unacceptable to me, as it is to them."
The fake patients had varying degrees of involvement and those who took part were asked to do so.
Staff working in the clinic that day were found to be "generally aware or soon became aware" of the incident and went along with it as they thought the health service expected them to.
The probe recommended the fake patients who did not organise the incident should not face disciplinary action, which the department agreed to.
However, those who organised it could face consequences.
The department said it does not have authority to take employment action against them but the health service has been asked to review evidence and determine if they should be counselled, have further training or face disciplinary action.
The investigation also recommended the health service do more to ensure a safe culture where people can speak up.
The incident was first raised by a whistleblower and some staff only took part in the department's probe on the condition of anonymity.
Ambulance Victoria's internal investigation into the involvement of the ambulance is underway.
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