When Jeff Beck's left armpit swelled to the size of a basketball a few days after he cut his finger at work, he had no idea a deadly flesh-eating bacterial infection was rapidly spreading through his body.

Now he's lying in an induced coma, fighting for his life at The Alfred hospital. 

It started on November 3 with flu-like symptoms which gradually worsened until the usually fit and healthy 55-year-old labourer from Moe couldn't get out bed for three days.

"Dad is the kind of guy who never complains about anything," his daughter Stephanie, 25, said.

"He doesn't drink. He doesn't smoke. He is never sick and he's always kept himself very fit from his work, but mum knew something was wrong when his armpit swelled up and he told her the pain he was feeling was 10 out of 10."

By the time the father of four arrived at the Traralgon Hospital he was septic.

Doctors diagnosed him with necrotising fasciitis, sometimes called "gas gangrene", which is a serious infection that occurs when bacteria enters the body through a break in the skin, eating away the soft tissue.

He had surgery to remove layers of dead tissue, which had turned black from the infection, before being airlifted to The Alfred where he remains in a critical condition.

Since then, he's undergone more than seven surgeries, with doctors removing a quarter of his torso and more than five kilograms of dead skin, muscle and tissue.

Mr Beck has been in an induced coma in the hospital's Intensive Care Unit since November 6.

He is given hyperbaric oxygen therapy twice a day to help stop the infection spreading and to treat his large open wound

His family is keeping a vigil at his bedside. 

The condition is thought to be fatal in about a quarter of cases and can spread extremely quickly.

Dr Deborah Williamson, an expert with the Doherty Institute, said sometimes patients could become ill and die within 24 hours.

And those that survived often sustained major disfigurations, amputations and loss of body function, as "the main treatment is removing the dead tissue".

Dr Williamson said necrotising fasciitis was associated with a number of different bacteria, which had sometimes been linked to the sea, and also battlefields, where dirt got into wounds.

Around 400 cases are diagnosed in Australia each year, according to the Australian Institute of Health and Welfare, with those with a weakened immune system at greater risk.

In 2015, Port Melbourne VFL player Sam O'Sullivan was hospitalised with necrotising myositis, a rare form of necrotising fasciitis.

At the time, it was said the 24-year-old was believed to be one of only seven people in the world to have survived the strain of superbug, and possibly the only person to have survived the disease without losing a limb.

Unlike a fast-growing outbreak on the Mornington Peninsula of a mysterious flesh-eating ulcer, there were no physical signs of necrotising fasciitis.

Doctors told Mr Beck's family that they believed the flesh-eating bug was able to enter into his body through a small cut on his left hand.

Mr Beck spends his days doing heavy physical work, including concreting and installing street signs, and the cut was seemingly so insignificant that he barely noticed it.   

"The doctors told us it is the most aggressive type of flesh-eating bacteria there is but my dad is fighter," Stephanie said.

"Every day they have removed more and more black tissue and muscle but say it's becoming less and less each day, so we are hoping that he continues to improve." 

Stephanie said the family has been told her dad will never be able to work as a labourer again and faces a long and painful recovery requiring multiple skin grafts down the left side of his body as his wound heals.

The family have started a GoFundMe page to raise money for his medical bills and long-term accommodation close to the hospital. 

In a matter of days, it's raised more than $14,000 toward a $17,500 goal.