The victims of last week’s thunderstorm asthma event.

A FREAK weather event that took Melburnians by surprise last week has claimed another two victims. Several others remain critical.

The death toll from last Monday’s thunderstorm asthma event climbed to eight on Tuesday, according to the Victorian Department of Health and Human Services.

It was previously reported that six people had died when stifling heat, a high pollen count, strong winds and moisture in the air combined to cause breathing difficulties for thousands of people in and around the CBD.

Tuesday’s victims have not yet been named.

More than 8500 people were hospitalised last Monday. Victoria’s ambulance service struggled to cope with the unprecedented spike in calls.

Among the victims were Hope Carnevali, 20, Omar Moujalled, 18, Apollo Papadopoulos, 35, and Clarence Leo.

Ms Carnevali died on the front lawn in the arms of family waiting for an ambulance.

Mr Moujalled was on his way when he lost his fight for life.

Paramedics tried to revive Mr Papadopoulos without success and Mr Leo died in the early hours of Tuesday morning.

Clarence Leo, with wife Amanda Leo, died on November 22 as part of the "thunderstorm asthma" event.

Clarence Leo, with wife Amanda Leo, died on November 22 as part of the “thunderstorm asthma” event.Source:Supplied

Thunderstorm asthma has been witnessed just four times in the past 30 years in Melbourne, a city that is susceptible because it is surrounded by parks and gardens.

It happens when pollen granules rupture from moisture in the air. They break up into hundreds of tiny particles that find their way into human lungs and make breathing difficult.

People who get hay fever are most at risk. For many sufferers, they had never experienced asthma in any form. They panicked, phoned triple-0 and waited for help.

Ambulance officers did the best they could, but resources were stretched to breaking point.

Ambulance Victoria released a statement on Tuesday afternoon, announcing an official investigation would be carried out. Executive director of emergency operations, Mick Stephenson, said Monday’s spike in emergency calls was unprecedented.

“We’ve essentially had a day’s workload within five hours,” Mr Stephenson said.

John Weiner, a consultant physician at AllergyNet, told Monday’s conditions were “the perfect storm” for Melburnians.

He said victims suffered “the same as any other asthma (sufferers), but it’s a dramatic event occuring quickly for people who haven’t had it before.”

Omar Moujalled, 18, and Hope Carnevali, 20, are two of the eight victims of thunderstorm asthma in Melbourne.