A deadly fungus that 'eats you from the inside out' is on the rise, which could affect millions.

Scientists are warning a lethal fungus that is capable of rotting tissue from inside the human body is spreading at alarming rates across the US and the world - and could spread even more due to climate change in the coming years.

Being airborne, the aspergillus group of fungi is almost impossible to dodge and its spores are so minuscule that people can inhale them without realizing.

The fungal mold thrives in warm and damp climates, affecting animals, livestock, plants and humans that come into contact with it.

Inhaling the life-threatening toxic spores can cause serious infections, particularly affecting the lungs in a condition called aspergillosis, which for vulnerable people can cause organ failure and fatalities.

A team of scientists from the University of Manchester have released a new paper on the matter, warning that climate change is threatening to increase the risk of infection and push into new parts of North America, Europe, China and Russia in the next 15 years.

An infectious diseases study in The Lancet published last year reveals fungal infections already kill around 2.5 million people every year, but a lack of data keeping means the figure could be even higher.

Co-author of the new study, Norman van Rijn, added that fungi are 'relatively under-researched compared to viruses and parasites', and is difficult to diagnose, yet the research by the university team found 'fungal pathogens will likely impact most areas of the world in the future'.

People with compromised immune systems, like patients with cancer, asthma, HIV, cystic fibrosis and COPD, as well as organ transplant patients, are especially at risk of health complications from breathing in fungal spores.

In such cases, the professor at the University of Manchester's School of Biological Sciences said the fungus 'starts to grow and basically kind of eat you from the inside out, saying it really bluntly,' reports CNN.

The deadly fungus has also already been found across several states in the US, such as Florida, Georgia, Louisiana and Texas, the Daily Mail adds.

California is said to be experiencing the highest exposure due to its humid climate and farming activity.

Meanwhile, major cities like New York and Los Angeles are at risk due to its dense populations and aging infrastructure.

The pathogens of Aspergillus flavus could increase by as much as 16 percent, spreading across the US, Europe and beyond, the researchers added, putting one million more people at risk.

And Aspergillus fumigatus could increase by an eye-watering 77.5 percent, exposing nine million people in Europe.

Medics warn people with weakened immune systems should avoid soil, gardening and moldy environments - and to wear masks where possible in dusty areas where fungi could grow.

Professor van Rhijn explained further to the Financial Times: "We're talking about hundreds of thousands of lives, and continental shifts in species distributions.

"In 50 years, where things grow and what you get infected by is going to be completely different."

Fungi are 'incredibly adaptable organisms,' the researchers note, which allows them to colonize new areas and withstand environment changes - even showing signs of resisting antifungal measures.

Rhijn added: "Changes in environmental factors, such as humidity and extreme weather events, will change habitats and drive fungal adaptation and spread.

"Raising awareness and developing effective interventions for fungal pathogens will be essential to mitigate the consequences of this."