Peter Jackson and Christian Rivers describe Mortal Engines' journey from novel to screen

When Sir Peter Jackson taps you to direct his next blockbuster, the instant reaction is a very human one - disbelief, then fear.

Christian Rivers felt that fear strongly, but of course he did it anyway.  And if he was scared, he was in good company.

"It's good that Christian is scared", says Sir Peter.

"Fear is actually good. Every time I direct a movie I am scared, you always are, and fear is actually a really good motivator."

The blockbuster is Mortal Engines, based on the Philip Reeve books set over a thousand years from now, where the worlds remaining cities - traction cities - are on gargantuan wheels, chasing down smaller towns to devour for much needed resources, and for their very survival.

The human heart of the books is the love story between the enigmatic rebel Hester Shaw on her quest for revenge and Tom Natsworthy, a rather naive Londoner who unexpectedly finds himself along for the ride.

As soon as Sir Peter read the books, he knew immediately he wanted to make them into movies. He set about writing the screenplay with his long-time writing and producing partners Philippa Boyens and Fran Walsh, then he roped in Rivers to direct.

Their own history is a typically Kiwi one and started over 20 years ago, when the now 44-year-old Rivers was still just a teenager.

"I sort of wrote him a letter and sent down pretty much every drawing I'd ever drawn," he says.

What Rivers didn't know - until now - is that his letter was a first for Sir Peter.

"Actually, this is the honest truth - that was the first bit of fan mail I ever got in my life."

A shocked and rather pleased Rivers told his long-time friend: "I didn't know that!"

"We were doing Braindead a couple of years later and I wanted to do storyboards," says Sir Peter.

"There were no professional storyboarding people around, so who do I get to actually sit with and draw? And I remembered the drawings that had come through the mail of dragons and monsters and other things.

"So we contacted Christian, who had just left school, so the timing was perfect."

The rest, as they say, is history; a history full of hobbits, apes and Oscars... and now, full of massive, rolling cities thundering across a barren future world.

It's a world that cinema audiences have never seen before.

Mortal Engines is also a world that had close to a thousand people - almost entirely local - working across 10 massive sound stages in three separate facilities in Wellington. For Sir Peter, pushing boundaries is the only way he knows when it comes to making movies and as far as he was concerned, Aotearoa was the only place to make it.

"The thing we all know about Kiwis is there isn't really anything impossible," says Sir Peter.

"If somebody says 'there's no way you're gonna be able to do that', you just roll up your sleeves and say 'give us a minute or two', and we figure it out."

Figure it out they did, Mortal Engines will roll into cinemas globally early next month.