The fire at St John of God Hospital in Mount Lawley was extinguished on Sunday afternoon, after a number of patients had earlier been evacuated.
Families with newborns calmly gathered around the grass area while on the southern side of the hospital a number of elderly patients were visibly stressed after being evacuated.
One woman excitedly shouted she had gone into labor outside the maternity ward, despite emergency service crews and police running around.
The small blaze, which is the second at the Mount Lawley hospital in a matter of months was believed to have started in a plant room.
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Firefighters from five stations rushed to the fire as well as around 20 police and St John Ambulance crews at the medical centre on the corner of Ellesmere Road and Thirlmere Road.
It comes just two months after an air conditioning unit sparked a fire and mass evacuation at the same site in November last year.
One patient, who asked to remain anonymous, said her heart was racing as people were ushered out of the hospital with smoke billowing from the building.
"I was getting a visit from my son-in-law and daughter when my son-in-law said 'can you smell smoke'", she said.
"We looked out the window and saw smoke. I just thought, 'what do we do?'. My heart is absolutely pounding."
Fire and Emergency Services district officer John Manocchio said the hospital was immediately evacuated.
"It was a confirmed 'fifth alarm' incident...the minimum response is five career fire and rescue trucks crews who investigated and located the fire," he said.
"The hospital was evacuated as a precaution.
"The fire was contained to the plant room and there is no long-term disruption to hospital services."
Mr Manocchio said the start of the fire was yet unknown.
He couldn't say if the fire was related to the blaze at the hospital two months ago.