A sixth person has died and six people remain in intensive care following Melbourne's thunderstorm asthma outbreak on Monday.
Eastern Health confirmed another person died following the outbreak on Monday but no other details have been released.
"There have now been six deaths that may have occurred as a result of conditions relating to the thunderstorm asthma events on Monday," a health department spokesman said in a statement.
More than 8500 people have received hospital treatment since Monday's outbreak.
Five patients remain in intensive care in Melbourne hospitals, three are in a critical condition.
Thunderstorm asthma is sparked when storms play havoc with pollen particles, which then affect even people who do not normally suffer from respiratory problems.
"Some [deaths] may be directly related to the thunderstorm asthma, some may have had other conditions that the thunderstorm asthma exacerbated," Victorian Health Minister Jill Hennessy said.
On Monday, heavy rain caused rye grass pollen to absorb moisture and burst, dispersing smaller particles that became trapped in people's lungs.
The department said hospitals were continuing to treat 20 people for a number of related conditions aside from those in intensive care.
The four named victims are Omar Moujalled, 18, Hope Carnevali, 20, Apollo Papadopoulos, 35, and Clarence Leo.