Caitlin Stasey plays the main character of Ellie in the $20million action film about teenagers who band together, guerilla-style, when their country town is occupied by a foreign army.

The 104-minute film, shot late last year in Raymond Terrace, Dungog and Maitland, has been rated “M” by the Classification Board for ‘‘violence, drug use and coarse language”.

The ‘‘mature’’ rating means the film is not recommended for under-15s but there is no legal restriction on who can see an ‘‘M’’ film.

Stasey, best known for her long-running role as Rachel Kinski on Neighbours, admitted to the Newcastle Herald that diehard Marsden fans might be upset by plot and character changes by the film’s writer-director, Stuart Beattie.

But she said an angry “F” word from Ellie and a cold-blooded shooting were added “for the sake of cinema”.

“With film, because it’s visual as opposed to a book where you imagine everything and imagine it vividly, you have to make it as graphic as possible to get people’s attention,” the 20-year-old said.

The first of Marsden’s seven Tomorrow novels for teens was published in 1993.

“As grotesque as it might sound, people are completely desensitised to violence now,” Stasey said.

“Even someone getting shot in the head, teenagers are like ‘big deal’. So we needed a moment that shocks people.”

Beattie and Stasey’s co-star Phoebe Tonkin will be at Greater Union Newcastle about 6.30 tonight for the film’s Newcastle premiere.