By day he fights crime, and by night Stefen Harris puts it into his own films.

The former Aucklander turned Christchurch policeman already has international awards to show for his burgeoning career as a film director, has rubbed shoulders with the Hollywood elite, and is eyeing up more success.

Following on from his mockumentary-style film The Waimate Conspiracy, which won best digital feature at New Zealand's film and television awards and top film festival awards in Australia and Canada, Mr Harris is set to release his second movie, No Petrol, No Diesel!

The "comedy ecological thriller" involves the mystery death of a small-town petrol station owner.

"There's sort of an enduring New Zealand myth about the guy who invented a water-powered car, and then the big oil company came in to suppress the invention or buy it from him, and he disappears in suspicious circumstances," Mr Harris said.

"If you tell that story in any pub anywhere in the country you will have people arguing about the details because everyone sort of knows it."

There may be comparisons between Mr Harris's work and his films - he also has a black comedy crime story in the pipeline - but life doesn't necessarily imitate art.

"I've very nearly been in the police 20 years now. So I guess we are shaped by our experiences, aren't we? I don't directly translate any stories out of things that happen at work or anything like that."

He balances his career as a policeman with film-making "with great difficulty". Most of his time off, nights and weekends are devoted to getting his films off the ground.

At age 15, as a student at Takapuna Grammar School, Mr Harris was edged out in a film competition by a teenage Peter Jackson.

He began writing novels, and one became The Waimate Conspiracy. It was made on a shoestring and its success surprised everyone.

"We thought we were making a quirky, low budget curiosity. I guess we had hoped that we might get it on television at some stage. To get a cinema release, that was a pretty major thing for us."

That success led him to spend time in the United States learning from New Zealand-born Hollywood director Martin Campbell, whose work includes the blockbuster James Bond films, Casino Royale and GoldenEye.

"I believe this was a better experience than any film school - seeing someone like Martin at the top of his game."

No Petrol, No Diesel! premieres in Christchurch on August 1.