British author Terry Pratchett File picture: Kirsty Wigglesworth/AP

London - A steamroller was used to destroy a hard drive containing unfinished works by late British comic fantasy author Terry Pratchett in accordance with his wishes.

"One lousy steamroller, 10 unpublished novels and look at all the trouble I'm in!" Rob Wilkins, the writer's long-serving assistant, said on Twitter on Wednesday with a photo of him in front of the steamroller.

Before destroying the hard drive, Wilkins tweeted that he was "about to fulfil my obligation to Terry".

He used a six-and-a-half ton vintage machine named "Lord Jericho" to roll over the hard drive at the Great Dorset Steam Fair last week, before a stone-crushing machine was used to finish it off.

Pratchett, who sold more than 85 million books worldwide in 37 languages, died in 2015 aged 66 after a long battle with Alzheimer's disease.

His Discworld novels about a flat world balanced on the back of four elephants standing on a giant turtle are some of the best-selling works in English fiction.

He wrote the first book in the series, "The Colour of Magic", in the late 1960s although it was not published until 1983.

Pratchett finished the 41st book in the series in 2014 before succumbing to the final stages of his disease.

Also read: Terry Pratchett: a reader remembers

The remains of his hard drive will go on display next month at an exhibition about the author at Salisbury Museum, near where he lived.

The museum's curator Richard Henry was cautious about the hard drive's contents.

"I know there was 10 unpublished stories that Terry was working on and it was his request that they were run over by a steamroller," he told AFP.

"But what exactly is in the hard drive, I just honestly don't know. And as a fan of Terry Pratchett I quite like the idea of it remaining a mystery."