Four in 10 people experiencing thunderstorm asthma symptoms had not been diagnosed with asthma yet most had suffered hay fever prior to last week's freak event in Victoria, an Asthma Australia survey has found.

Eight have died, and one remains in intensive care more than a week after a thunderstorm surged across Melbourne, carrying pollen that strong winds and rain broke into tiny fragments.

The tragic deaths of at least six people, apparently from thunderstorm asthma, highlights the risk from environmental hazards, even in seemingly safe urban centres in developed nations like Australia.

Following news that an eighth person, Ranjith Peiris, has died and one remains in intensive care from Melbourne’s thunderstorm asthma epidemic, experts are surveying the fallout from what has quickly become the worst event of its kind in world history.

A perfect storm of factors that triggered a mass asthma event and claimed at least six lives in Melbourne has perplexed health experts, who believe climate change may be the missing piece in the puzzle.

A sudden drop in temperature in Melbourne on Monday evening from peaks of 35 degrees Celsius brought with it severe thunderstorms and triggered a mass asthma event that left hospitals struggling to treat 8,500 patients.

A fifth person has died and six people continue to fight for life following Melbourne’s fatal thunderstorm event on Monday.

A fourth death has been attributed to Melbourne’s “thunderstorm asthma” emergency on Monday night, and it was lucky there were not more, according to the state’s health minister.

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

Three people are still fighting for their lives after Monday night's sudden outbreak of "thunderstorm asthma", which saw 8500 people treated in hospitals across Melbourne.