But his famous novel-series Tomorrow, When the War Began is hitting the big time again.

Marsden is a children's writer, school principal and founder of Candlebank, an alternative, independent school in Romsey.

About 17 years ago, he wrote the No.1 best-seller, which was the first book of a seven-part war series. It has now been turned into a $20million Australian movie, directed by Stuart Beattie and starring Caitlin Stasey and Lincoln Lewis.

It premiered in cinemas last Thursday. "I might say that the actors are a lovely group of kids. They are humble, they are very down to earth, very Australian," Marsden told the Weekly.

"There's a couple of really great scenes, funny moments in the movie which I didn't expect. It is generally pretty good."

The movie follows eight teenagers on a camping trip when foreign invaders take over the country.

The movie hype has created a spike in book sales. To keep up with demand, 40,000 more copies have been printed.

More than 3000 books were sold in one week in the lead-up to the movie's premiere.

Marsden didn't expect such success. "I've had hundreds of offers from film companies all over the world since the book first came out, but I kept saying no," he said.

"I realised this is a chance that not many people have [read the book] and maybe I should take it. I didn't want to go to my grave missing out on an opportunity. The worst thing that could happen is that they make a terrible film and it would be forgotten."