The director is in a race against time to complete his 3.2 million-US-dollar film "3-D Sex and Zen: Extreme Ecstasy", which is due for release in May. It is a race because Italian director Tinto Brass has already announced he will produce a 3D remake of his 1979 erotic film Caligula.

Adding to the pressure, Hustler is making a pornographic spoof of 3D science fiction blockbuster Avatar, the highest-grossing movie of all time and the film that heralded the beginning of the mainstream 3D boom.

Producer Stephen Shiu, a one-time newscaster, is still betting his picture will be out before them both and make film history. "I don't think they can beat us," Shiu said. "This is the future of the movie business -- it's human nature to want to see things in 3D."

 Still, the challenges are legion when making a film that is more technically complex than a regular movie and that features orgies and actors having sex while swinging on chains.

Three-dimensional film-making requires stronger lighting than traditional movies and limits the ability of cameras to move around quickly.

Saori Hara, 22, one of the two female Japanese stars, said the film's technical complexities made it tougher than her previous movies. "I have to work harder to not let the audience down," she stated during a break, adding: "I hope people all around the world will see this movie."

Bashful male actors make the job even tougher, although Shiu's imported Japanese talent is helpful, he says. "I have great respect for the Japanese girls -- they can work 18 hours a day so they get very exhausted, but these two are very good," he said. "The men are shy, very afraid. But the girls help out."

Leading man Hiro Hayana, 35, admits starring in his first erotic film is daunting, although he had no complaints about a scene in which he is tasked with satisfying 100 women -- many flown in from Thailand due to a lack of willing talent in conservative Hong Kong. "I felt like the king of the world," Hayana said.

 The movie is largely being filmed on a set modelled on a cave-turned-sex den equipped with illuminated fake rocks, erotic murals, and animal skin rugs -- as well as a few faux Ming Dynasty antiques.

Loosely based on a classic of Chinese literature, The Carnal Prayer Mat, the movie chronicles the story of a young man who, after being introduced to the erotic world of a nobleman, realises his ex-wife is the love of his life.
Although mainland Chinese censors are almost certain to block the movie's screening, it has sparked wide interest in other Asian markets, including Japan and South Korea, as well Europe, and the United States, Shiu said.

The film is first due for theatrical release -- partly in order to curb illegal downloading -- with a 2D version to follow for home viewing.

Shiu insists the film is female-friendly since it is more about love and romance than plotless sex scenes. In fact, the producer figures it outdoes his own 1991 "Sex and Zen", still the highest-grossing Hong Kong adult movie of all time.

"I wanted to make a good commercial film even without the sex scenes," he said. "Visually it is very spectacular -- that is why it is worth doing in 3D. It is funny and very touching at the end. Actually, it's one of the best scripts I've ever written."