The death toll from Victoria's freak thunderstorm asthma event is now at eight, after two more people died.

Two more people have died from Melbourne's freak thunderstorm asthma event, taking the death toll to eight.

The two had been in a critical condition in intensive care before they died overnight and on Tuesday morning.

One person is still in a critical condition in hospital and getting specialist care after the storm on Monday last week.

"This was a tragic and unforeseen event and hospitals are continuing to treat seven people for a variety of respiratory and other related conditions," a Department of Health and Human Services spokesman said on Tuesday.

Every available ambulance in Melbourne was sent out on calls during the storm, and more than 8500 people were admitted to hospital.

The state government has since announced an extra $500 million funding over five years to employ 450 more paramedics, put more new ambulances on the road and build 15 new and upgraded ambulance stations.

The freak event started when pollen blew into Melbourne from the state's northern pastures on a blustery day.

Pollen grains absorbed moisture during the evening thunderstorms and then burst into hundreds of tiny allergenic fragments, which are small enough to penetrate deep into the airways.

Ambulance Victoria had a full day's emergency calls crammed into just five hours when the storm hit.

The Inspector-General for Emergency Management is leading a review examining how Ambulance Victoria and emergency services responded and how the community was notified.
The review will also investigate the deaths.