For three hours between midnight and 3am on Wednesday the service advised there was likely to be delays in ambulances arriving because of an extremely high demand in the metropolitan region.
"Our priority is to provide care to Victorians who require life-saving assistance," Ambulance Victoria said in a statement.
They reminded people to call Nurse On Call on 1300 60 60 24 or visit their local GP if their case was not an emergency.
Ambulance Employees Association Victoria secretary Brett Adie told AAP there was usually more than one cause for these types of events.
COVID-19 is somewhat to blame, he said, with paramedics testing positive and others in isolation leading to an inability to fill shifts and get ambulances on the road.
"It was identified pretty early that there was going to be a problem last night with staffing," Mr Adie told AAP.
But he said the virus was not the only problem, noting ambulance case numbers now are no higher than projections forecast back in 2019.
He said hospitals have been under pressure since before the pandemic and that can lead to delays in transferring patients, which in turn affects ambulances on the road.
Mr Adie has called for a better referral process, improved options for leaving people at home, and using on-call services to put people in touch with a doctor when they do not need to be taken to hospital.
He said changes were starting to happen but had to be implemented faster and should have been done sooner.
"We've become reactive instead of proactive," he said.
"We were resources for yesterday, not for tomorrow.
"We're failing the community - the community have higher expectations. And fair enough, so they should."
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