Five people are critically ill and more than 60 people remain in Victorian hospitals after Monday night's "thunderstorm asthma" crisis.

Four people died during the unprecedented health emergency, which overwhelmed the ambulance service and sent thousands of people to hospitals with respiratory problems and asthma attacks. There are fears more deaths will be attributed to the disaster.

On Friday afternoon, the department of health said "a number of people" remained in intensive care units because of the outbreak, with five listed as critical. More than 60 people are still in hospital because of sickness related to the event.

The department said 8500 people went to Victorian hospitals on Monday and Tuesday after stormy weather conditions caused pollen to explode in the air, triggering breathing problems for many people across the state, including those without a history of asthma or other lung conditions.