The mother of a young woman who died during last year’s thunderstorm asthma event has recalled her daughter’s desperate pleas for help as she died outside the family home.

Hope Carnevali, 20, was one of nine people who died as a result of the catastrophic weather event on November 21 last year.

Thunder and rain battered Melbourne as five storms combined into one front that swept across the city from the west, but the most threatening factor was unseen.

Electrically charged rye grass pollen exploded, which created tiny particles small enough to enter people’s lungs and trigger asthma symptoms.

Just after 6pm Ms Carnevali, who suffered from asthma, began to struggle to breathe at her family’s Hoppers Crossing home.

Hope Carnevali died during the thunderstorm asthma event last year. (60 Minutes)

Her mum Danielle called an ambulance but as they waited, her daughter began to deteriorate.

“It’s indescribable, I’m watching my daughter disintegrate, barely able to move,” the grieving mum told Tara Brown on 60 Minutes tonight.

“It was traumatic.”

As the wait for an ambulance stretched to 30 minutes, Ms Carnevali considered taking her daughter to hospital herself but was told to stay by an operator.

“She started turning blue,” she told Brown.

“Just before her last breath, (she said) ‘Mum I’m dying, mum I can’t breathe, mum help me’.

“To not be able to help her, as a parent that is the hardest thing you can ever go through.”

Hope’s conditioned worsened and she died on the lawn outside the home before an ambulance arrived.

“I think the hardest part as a mum is that I had that chance of saving my daughter taken away from me,” Ms Carnevali said.

“Had I been told that an ambulance wasn’t in the vicinity, it wasn’t dispatched, they had none left, I would have put her in that car in a heartbeat.

“I would have had her at that hospital, which is about six minutes away, and she would still be here with us today.

“I have to live with that guilt because she asked me to help her, and I didn’t help her.”

In addition to the nine fatalities, 8500 people were taken to hospital. It was the most severe case of thunderstorm asthma ever recorded anywhere in the world.

Paul Holman, Ambulance Victoria’s director of emergency management, said an emergency call was being made every four seconds at the peak of the storm.

“We intended to get to everyone possible – you call us, we will come,” he told Brown.

“We had an unprecedented emergency, a major disaster.

“We will learn - how can we get it better next time?”

In response to the crisis, the Victorian government ordered an inquiry and has developed a $15.56 million package to better predict and respond to large-scale health events.