Tracey Corbin wrote to the Labor prime minister in 1985 after struggling to deal with the death of her grandmother.

Mr Hawke wrote back in July that year saying her question about why we all die was "very hard to answer".

"Some people die because of unfortunate accidents, sometimes because they become so ill that doctors are unable to help them recover," he said, according to a copy of the letter posted on Twitter in the hours after Mr Hawke's death on Thursday.

"Perhaps when we grow very old our bodies get worn out, or certain parts break down, like parts in an old car.

"None of us can be sure of how long we will live. Because this is so I think you should try not to think too much about dying but think about all the nice things around you that make life so precious to us all."

The girl, now known as Tracey Corbin-Matchett, said his letter to her is "my most treasured childhood memory".

The post was trending strongly on multiple social media platforms on Friday.

Australian Associated Press