A rare condition known as thunderstorm asthma sent hundreds of people to hospitals in Australia's second-largest city, and four deaths had been confirmed by Wednesday.

Family confirmed Clarence Leo, a nightclub bouncer and father of two, died at home early Tuesday morning after the wild thunderstorm in Melbourne on Monday night caused rain-sodden ryegrass pollen to explode and disperse over the city. The pollen caused asthma attacks in some patients who had never suffered from asthma before.

Ambulance Victoria responded to more than 1,870 cases, which was six-times the usual workload for a Monday evening, spokesman Mick Stephenson said.

Professor George Braitberg, head of the Royal Melbourne Hospital's emergency department, likened the scene in the hospital on Monday night to a war zone.

Seven asthma patients had been transferred to the hospital's intensive care unit, he said. Some patients had never before had asthma attacks, he said.

"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," Braitberg told Ten Network television.