AS Nicole Kidman and Russell Crowe begin rehearsals for their first movie together, the Australian film’s director, Baz Luhrmann, said he was still missing a key cast member.

Luhrmann yesterday put out a casting call for an indigenous boy, aged 7-10, to join the cast of his untitled Australian epic, set in Darwin in the 1930s.

The director, best known for the musical Moulin Rouge, said Kidman and Crowe, whose characters become involved in a love triangle, will begin rehearsing in Los Angeles in two weeks.

With a rumoured budget of $40million, the movie will be shot in Australia and is set to be one of the most expensive and adventurous local films.

Speaking from the north Queensland town of Bowen, which may double as Darwin, Luhrmann described the film as an epic on the scale of Gone With The Wind, Out Of Africa or Giant.

“It’s a classic emotional romance between two characters,” he said. “We have some of the most extraordinary landscape on the planet and we want to get two of the most extraordinary actors in the world and put them, acting, in that landscape.”

While the movie, co-written by Luhrmann and Australian screenwriter Stuart Beattie (Collateral), is not based on a true story, Luhrmann said events such as the bombing of Darwin in World War II would provide a backdrop to the story.

While Darwin’s wharf may be used for filming, financial restrictions may force more out-of-the-way locations such as the Kimberley to be recreated at Sydney’s Fox Studios.

Shooting is expected to begin in the next few months – by August at the latest because of the wet season – and Luhrmann is expected to announce the name, location and other cast members in the coming weeks.

The director, who has been working on the movie for the past seven years, said it came from a passion shared between himself, Kidman and Crowe to “do something purely Australian on a scale the world hasn’t seen before”.

“It was kind of, ‘What can we do at home?’ because we love being here,” he said.

Sydney-based Luhrmann said he would use an Australian crew, including his wife and creative partner, Oscar-winning costume and production designer Catherine Martin. “CM and I just put our domestic life in order so that we can work at home and make something, give as much as we can back to the country and be part of it,” he said.