This week, members of the "Mad Max 4: Fury Road" production crew declined to disclose details of the movie, saying everyone involved had been forced to sign confidentiality agreements. But on Thursday a South African crew member said skilled stuntmen were undergoing training in Cape Town.
It's also believed that Theron and Hardy are being subjected to rigorous training.
The SA crew member said specially modified off-road vehicles were recently shipped from Australia to South Africa.
The containers, stored under tight security in Port Kembla, New South Wales, were then transported overland to Namibia three weeks ago.
The fleet was designed by Ford Australia's Research Centre. "At this point, everything is on a need-to-know basis," said the crew member.
The production, involving a crew from the US, SA and Namibia, is expected to generate up to 500 jobs.
Oscar-winning director George Miller recently told ABC News in the US that "the reason the movie is so big is that it's got just a huge number of stunts, and we're trying to do stuff that I believe people haven't done before".
Miller, who also directed animation blockbuster "Happy Feet", is expected to start filming next month.
The secret location has already been transformed into a post-apocalyptic wasteland.
The original 1979 Australian movie starred Mel Gibson, who was unknown at the time.
It became a top-grossing film and spawned two sequels, "Mad Max 2: The Road Warrior" in 1981 and "Mad Max: Beyond Thunderdome" in 1985.
In a recent interview, Hardy said the production was shrouded in secrecy.
"These things are always binded to secrecy, and I think that's a good thing for the film anyway.
"I'm not allowed to give away anything," he said.
Namibia was a second choice for Miller, who was set to start filming in the small Australian town of Broken Hill late last year.
But the heaviest rainfall in 75 years ruined his plans.
Just R20 for the first month. Support independent journalism by subscribing to our digital news package. 