Storm clouds gathered Monday over Melbourne, Australia, before a major thunderstorm unleashed an outbreak of a rare form of asthma. Australia Bureau of Meteorology

Six people have died and five remain on life support after a rare condition known as thunderstorm asthma struck Australia's second-largest city.

The sixth victim, who has yet to be identified, died in hospital on Saturday night from medical complications stemming from a wild thunderstorm that struck Melbourne on Monday night, the health department said.

Another five patients remain in intensive care in Melbourne hospitals, with three listed as critical. And a further 12 patients were in hospitals with less serious respiratory and related conditions.

According to the Herald Sun newspaper four of the victims have been identified as Hoppers Crossing law student Hope Carnevali, 20; Greenvale high school student Omar Moujalled, 18; Noble Park father-of-two Clarence Leo and Epping’s Apollo Papadopoulos, 35.

A fifth patient, who passed away in the Northern Hospital on Friday night, is yet to be identified.

Monday's storm caused rain-sodden ryegrass pollen grains to explode and disperse over the city, with tiny pollen particles penetrating deep into lungs. Around a third of patients who suffered asthma attacks on Monday reported never having asthma before.

The storm overwhelmed emergency services and hospitals in the city of 4.5 million people, with 8,500 receiving hospital treatment.

The world's first recorded thunderstorm asthma event occurred in Melbourne in 1987, when hospitals reported a five-fold increase in asthma cases.

Similar events have happened in the United States, Canada, Britain and Italy. The last major event in Melbourne was in November 2010.

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