A fifth person has died following Melbourne's thunderstorm asthma event on Monday.
Six other patients are still being treated in intensive care, four of them who are in a critical condition.
"We are now aware five deaths may have occurred as a result of conditions relating to the events," Department of Health and Human Services spokesman Travers Purton said in a statement on Saturday.
The latest victim, believed to be a woman, died at Northern Hospital in Epping on Friday night.
A hospital spokesman said the asthma thunderstorm led to other medical complications for that patient.
"During this difficult time, our thoughts are with the patient's family and friends. It would be inappropriate to make any further comment," he told AAP.
Included in the five are Noble Park father-of-two Clarence Leo, 35-year-old Apollo Papadopoulos, law student Hope Carnevali, 20, and Year 12 student Omar Moujalled.
The Inspector General for Emergency Management will investigate the cause of those deaths and his findings will form part of an overarching review that will examine how Ambulance Victoria and emergency services responded and how the community was notified of the unfolding crisis.
Hospitals across Melbourne are continuing to treat another 20 people for a variety of respiratory and related conditions.
Across Monday and Tuesday, they treated more than 8500 patients.
At one point on Monday evening, there were 140 simultaneous "code one" cases.
The perfect storm event saw a high pollen count and thunderstorm conditions combine to produce tiny particles in the air that penetrated deep into people's airways, causing attacks for asthma sufferers.
A team of experts is now trying to determine whether severe asthma storms can be predicted in the future.
They occur when grass pollen, dust and other allergens are blown ahead of a storm front and then rupture into tiny particles that can penetrate deep into people's airways.
