Two people died waiting for ambulances in Melbourne last night after an unprecedented outbreak of a phenomenon called "thunderstorm asthma".
Paramedics struggled to cope with demand and hospitals declared a disaster response situation.
One of the victims was a 20-year-old man who reportedly waited half an hour for an ambulance.
Temperatures reached the mid-30s before a dramatic change in temperature, with thunderstorms sparking an unprecedented number of asthma attacks.
Meteorologist David Brown says the attacks come after pollen particles multiply dramatically in thunderstorms.
Paramedics in Victoria were flooded with more than 1900 calls in five hours - more than six times their usual load.
They ran out of ambulances, forced to call in police officers and field doctors to get patients to hospital.
Ambulance Victoria is now reviewing its response systems.