The deaths of two people who reported respiratory issues during Melbourne's "thunderstorm asthma" event will be investigated by health authorities.
A 20-year-old person in Melbourne's west and a Werribee resident died as paramedics dealt with an unprecedented 1900 emergency calls in five hours on Monday evening.
Hundreds more patients streamed into hospitals.
The Royal Melbourne Hospital emergency department dealt with a record 335 patients in 24 hours - 130 more than on a regular day.
More than 215 people presented with thunderstorm asthma causing an "unprecedented surge", the hospital said.
"This is just a very timely reminder that we have to continue to invest, we have to continue to do more."
The Royal Children's Hospital had 500 patients attend with 60 still waiting to be treated at midday on Tuesday.
The day clinic at St Vincent's Hospital had to be opened to deal with 100 extra patients.
One of those who died had to wait 30 minutes for an ambulance.
Victorian Health Minister Jill Hennessy says the storm put unprecedented demand on the health system.
She's waiting for details of the two deaths.
"There will no doubt be a full review of what occurred last night and what the clinical outcomes were as a result of last night," Ms Hennessy told reporters on Tuesday.
The health system's response to natural disasters will also be reviewed.
Mick Stephenson, director of emergency operations at Ambulance Victoria, said the organisation will complete a full clinical review within a few days as to whether the two deaths were related to ambulance delays and the asthma event.
Paramedics on Monday evening received five and a half times more calls than on a regular night.
Between 7pm and 7.15pm a new patient called every 4.5 seconds.
The demand led to off-duty paramedics and managers, including Mr Stephenson, being recalled to attend calls.
Police and the MFB also helped.
Premier Daniel Andrews says the government has already boosted ambulance budgets and paramedic numbers.
"This is just a very timely reminder that we have to continue to invest, we have to continue to do more," he told reporters on Tuesday.
Melbourne's last major thunderstorm asthma event was in 2010.
There was also an episode in 2011 but both previous incidents were less significant than Monday's emergency.
Thunderstorm asthma is caused when dust and pollen is blown in or ahead of a thunderstorm.
The moisture then causes the pollen grains to burst into hundreds of fragments tiny enough to penetrate deep into the airways.
Pharmacies in Melbourne reported a rush on asthma medication ventolin.
The thunderstorm didn't only cause health problems with more than 300 calls to SES for fallen trees and building damage.
Meteorologist Stephen King said localised wind gusts at St Kilda reached almost 100km/h while the late afternoon cool change caused the temperature in Melbourne to drop 10C in 10 minutes.
Asthma and hayfever sufferers can now breathe a sigh of relief with Melbourne's pollen count forecast to be in the low and moderate range for the rest of the week.