Melbourne has been hit with a thunderstorm asthma crisis which has left six people dead and others in a critical condition after heavy rain and wind struck the city on Monday.
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Thousands of people have suffered pollen allergy asthma attacks in the state of Victoria and hospitals are stretched to their limits, with thousands of residents phoning to report breathing problems.
The Herald Sun reports that 8,500 people were treated in hospitals for asthma in 24 hours.
In a statement on Sunday, Australia's health department said: "There have now been six deaths that may have occurred as a result of conditions relating to the thunderstorm asthma events on Monday."
Included in the six people who died are father-of-two Clarence Leo, 35-year-old Apollo Papadopoulos, 20-year-old law student Hope Carnevali and student Omar Moujalled.
Thunderstorm asthma is only known to have occurred several times before in Australia.
According to the Met Office, the rare outbreak is not yet fully understood as it is caused by a combination of factors. It is triggered during the summer by a combination of large storms caused by converging masses of air, high humidity and possibly high levels of air pollution.
As large thunderstorms pass over the land, they draw up pollen and spores, with very high humidity in the cloud causing these to break into pieces and penetrate deep into the lungs.
The Guardian reports that Melbourne has suffered the most lethal episode of thunderstorm asthma on record.
Professor Anthony Seaton, from the University of Aberdeen, told the newspaper: "I don't know of any event as severe as this."
Thunderstorm asthma attacks have previously been recorded in the UK, Italy and America.
In June 1994, a large outbreak of thunderstorm asthma in London led to 640 patients overwhelming hospital emergency departments.
Experts have warned that climate change is likely to bring an increase in frequency of the deadly storms.