The koala rescued by a woman who used the shirt off her own back has died due to the severe burns sustained in the bushfire.

Video of the koala's dramatic rescue during NSW's bushfire crisis earlier this month went viral and Toni Doherty was hailed a hero for helping the distressed animal.

The koala, named Ellenborough Lewis after the area it was found and Ms Doherty's grandchild was taken to the Port Macquarie Koala Hospital.

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But his burns proved too severe and the hospital made the difficult decision to put him down on Tuesday.

"We placed him under general anaesthesia this morning to assess his burns injuries and change the bandages," the hospital posted on Facebook on Tuesday.

"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."

The koala had been receiving round-the-clock care and substantial pain relief for burns to his hands, feet, arms and the inside of his legs.

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Thousands of hectares of koala habitat across northern NSW and southeast Queensland were destroyed in the recent bushfires.

More than 350 of the marsupials are feared killed in the disaster.

The Port Macquarie Koala Hospital has been inundated with support and donations from the public, saying it now has enough supplies for the next decade.