Australia's largest milk bank is running out of milk as demand for its service soars to unprecedented levels.

The Queensland Milk Bank supplies about a dozen hospitals across the country with breast milk that has been donated and then pasteurised.

Dr Pieter Koorts, the director of neonatology at the Royal Brisbane and Women's Hospital (RBWH) where the milk bank is based, said there is currently less than 100 litres in the bank.

He said that was partly due to unusually high demand last month when the bank fed 51 babies at the RBWH alone.

"Fifty-one babies can go through quite a lot of milk pretty quickly," Dr Koorts said.

"We just pasteurised 85 litres in the last fortnight, so it does disappear pretty quickly, and we always like to have a bit of a buffer just in case there's an increase in demand."

The Queensland Milk Bank supplies donated breastmilk to hospitals in three states. ( Supplied: Queensland Milk Bank, RBWH )

Dr Koorts said the donor milk was offered to babies 34 weeks or younger, and that those aged between 23 and 28 weeks are at the highest risk.

"Whether you call it food or medication, it is life saving," he said.

"It's not just nutrition, it really is prevention of death and severe morbidity."

Increased demand

Since the Queensland Milk Bank started five years ago its output has increased from about 200 litres of pasteurised breast milk a year to more than 1,000 litres annually.

Dr Koorts said it was the biggest and fastest growing milk bank in Australia and the only one permitted to supply other hospitals.

Agreements are in place with about 12 hospitals in New South Wales, Tasmania, and throughout Queensland.

But Dr Koorts said he expected the distribution network to broaden with the recognition that for these fragile lives, donated breast milk was the next best option to a mother's own milk.

He said pre-HIV, many hospitals had unofficial milk banks until it was realised that some diseases and viruses were transmitted through breast milk.

"More recently people have been using formula in lieu of mother's own milk, and for pre-term babies, it's a death sentence.

"They can get either very sick, or die, or take such a long time to full feeds and they stay longer in the end so it's quite devastating to feed pre-term babies formula."

Dr Pieter Koorts says donated breastmilk can be life-saving for pre-term babies. ( Facebook: Queensland Milk Bank )

While Dr Koorts hoped for all hospitals around the country to be able to access the donated milk regardless of location, but the service that does not come cheap, with receivers being billed $500 per litre.

"We still have to charge them a processing fee and money to be able to supply them," Dr Koorts said.

"The gains you make by having kids go home earlier or get up to full feeds earlier or getting sick and not having to be treated is far outweighed [compared to the] cost.

"A day in ICU costs you about $4,000, a day in special care is about $1,500 so if you can get a kid home a week earlier because you've got them onto feeds quicker, you've saved that money right there."

Bulk bundle, no stress

Sunshine Coast mum Kassandra Reynolds became a donor to the Queensland Milk Bank after having her son Romeo. ( Supplied: Kassandra Reynolds )

Kassandra Reynolds, who welcomed her second child five months ago, recently did her first "bulk" drop of breastmilk to the milk bank via the Sunshine Coast University Hospital.

"I was just lucky enough to have an oversupply when my son was born and I knew that I had to donate," she said.

The Sunshine Coast mum is one of more than 400 donor mothers who have contributed nearly 6,000 litres of breast milk to the Queensland service since it began five years ago.

Those donations have helped more than 1,600 pre-term babies.

When Ms Reynolds' daughter Delilah was born six years ago she saw firsthand how difficult it was for mothers of premature babies to feed their young.

"We saw these tiny little premmie babies and mothers trying to get a drop of milk to feed," she said.

At the time she wanted to help by donating her excess supply, but the milk bank did not exist.

When it opened a year later, Ms Reynolds and husband Noah donated $5,000 to the new facility and now, five years on after her second child, she is finally able to donate her own breastmilk.

This week Ms Reynolds will take her 40-odd bottles of frozen breastmilk, each containing between 40-80 millilitres.

"They send you the bottles, the freezer bags and the labels … if you've got the system going already, it's easy," she said.

"The smallest amount can help those babies immensely."

Sunshine Coast mum Kassandra Reynolds gathers about 40 bottles of breastmilk that she's donating to the Queensland Milk Bank this week. ( Supplied: Kassandra Reynolds )

Not your average milk run

Dr Koorts said generally the donors need to be near a city or larger regional hospital where the frozen milk can be retrieved in timely manner.

"We also have mums who store it up in their freezers and drop it off in the parking lot as they drive through," he said.

"They drop off on a weekly or fortnightly basis."

The milk can be kept frozen for three months before it needs to be pasteurised at the Brisbane-based bank.

Dr Koorts said that process killed most bugs.

Demand through the Queensland Milk Bank is soaring with about 1,000 litres of breastmilk pasteurised in these machines annually. ( Supplied: Queensland Milk Bank, RBWH )

"You heat the milk up to 62.5 degrees centigrade for 30 minutes and then cool it down," he said.

"Milk is tested before and after pasteurisation … taking samples for microbiological testing to ensure that the milk that we end up providing to a very fragile infant is as sterile and safe and clear as it can be.

"Any bacterial growth that occurs pre or post pasteurisation we'll dump that entire batch because there's potentially too many bugs in there."

The pasteurised milk is then bottled, frozen and kept for up to three months ready to be dispatched.