A volunteer firefighter in Australia has been charged over an alleged arson incident on the south coast.

The New South Wales Rural Fire Service said it has immediately stood down the 19-year-old man.

Police there have charged him with seven counts of cause fire and of recklessly spreading it.

Rural Fire Service Commissioner Shane Fitzsimmons said they have zero tolerance for arson.

"Over the past few weeks, we've seen firefighters going above and beyond in difficult and dangerous conditions.

"Our members will be rightly angry that the alleged actions of one individual can tarnish the reputation and hard work of so many.

"This type of alleged behaviour is the ultimate betrayal of our own members, and of the broader community.

"Arson is a dangerous and criminal act. It isn't tolerated by society. And it's not tolerated by the RFS, or our members."

He added: "The community has the right to be disappointed but we should not let it detract from the incredible work that firefighters have done in protecting and saving so many homes during unprecedented conditions."

Huge fires have burned through millions of acres of farmland and bush in New South Wales, in what is one of the most devastating starts to a fire season in history.

There have been a number of deaths and hundreds of homes have been destroyed. The state is also suffering some of the highest levels of air pollution on record.

Meanwhile a koala that was dramatically rescued from bushfires was put to sleep on Tuesday.

Footage of Toni Doherty carrying the injured animal from the raging fires went viral on social media.

She used her shirt to protect the animal from the heat and smoke after rushing in to help.

He was taken to the nearby Port Macquarie Koala Hospital (PMKH) where he was treated for serious burns to his hands, arms, feet and legs.

But in a Facebook post, the hospital said it had taken the difficult decision to put the marsupial, named Ellenborough Lewis, to sleep.