4 killed by rare 'thunderstorm asthma' in Melbourne

"I've been an emergency physician for about 35 years, worked in a number of hospitals, and I can say, hand on heart, that I have not seen this before."

Four people have been confirmed dead from a rare condition known as thunderstorm asthma that sent hundreds of people to hospital in Melbourne.

The wild thunderstorm caused rain-sodden ryegrass pollen to explode and disperse over Australia's second-largest city on Monday night, and the pollen caused asthma attacks in patients who had never suffered from the condition before.