Ellenborough Lewis, a badly burnt koala that was rescued from a NSW bushfire, has been put to sleep after his burns worsened overnight.

Lewis received worldwide attention after NSW grandmother Toni Doherty was filmed by a 9News cameraman rushing into burning bushland in Port Macquarie to rescue the marsupial, estimated to be 14 years old.

"We were there this morning. We are naturally very sad about this, as we were hoping he'd pull through but we accept his injuries were severe and debilitating and would have been quite painful," Peter Doherty told 9News.com.au, speaking on behalf of his wife Toni.

© Supplied Ms Doherty was filmed rescuing Lewis in bushfire-ravaged Port Macquarie. "We would always defer to the recommendation of the staff at the Port Macquarie Koala Hospital."

The Port Macquarie Koala Hospital confirmed the news in a Facebook post.

"Today we made the decision to put Ellenborough Lewis to sleep. We placed him under general anaesthesia this morning to assess his burns injuries and change the bandages," the hospital said.

"We recently posted that burns injuries can get worse before they get better.

"In Ellenborough Lewis's case, the burns did get worse, and unfortunately would not have gotten better.

"The Koala Hospital's number one goal is animal welfare, so it was on those grounds that this decision was made.

"We thank you for your ongoing support."

© Today Lewis had bad burns to his stomach, chest, feet and legs.

After Ms Doherty took the shirt from her back to wrap Lewis in, it was found he had severe burns to his feet, legs, chest and stomach. She named the koala after one of her grandchildren.

"The poor koala, he was crying and screaming, because he was being burnt. He was burning underneath, on his little back legs... I've never heard a koala before. I didn't realise they could cry out. It was just so heart-rendering," Ms Doherty told Today after the rescue.

Koalas in Port Macquarie have been particularly hard hit by the bushfire crisis. In late October, it was estimated that 350 animals died out of a population of 600.

Donations from the Australian public have flooded into the Port Macquarie Koala Hospital, as the iconic Australian animal faces an uncertain future.