HONG KONG (Reuters) - On the leafy fringes of Hong Kong in a shabby film studio, a nude ponytailed actor stretched out on animal-skins with his lover as the cameras rolled in a set evoking a subterranean sex lair in ancient China.

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Turning away from a slightly blurred high definition TV screen as the actors writhed, director Christopher Sun shouted “cut” whilst yanking off his 3-D glasses. “Good” he yelled.

No ordinary porn flick, “3-D Sex & Zen: Extreme Ecstasy” is being touted as the world’s first IMAX-3-D erotic film.

First out of the gates, the soft porn Hong Kong film comes as the stricken industry, hit hard by free Internet porn in recent years, turns to 3-D as a potential money-spinner, following on from the success of Hollywood blockbusters such as James Cameron’s Avatar.

“Somehow when you’re doing a 3-D movie you always want to make an impressive image because the viewers ... are going to buy tickets with double or even triple the ticket price to get into a world they’ve never seen before,” said the U.K.-educated Sun

“It’s not just erotica, they want some ‘wow factor!.’”

Based on a classic Chinese erotic text, “The Carnal Prayer Mat,” the $3 million film follows a young man as he befriends a duke and enters a world of royal orgies and other sexual peccadilloes.

The producers are hoping the erotic period drama will prove a titillating hit with 3-D-glasses-wearing audiences and help develop a lucrative, niche film market.

“It’s because it’s forbidden in China, (that there) is so much enthusiasm in China for this film,” said film maker Stephen Shiu, who was responsible for the original 1991 erotic film “Sex and Zen,” which grossed over USD$2.6 million and held the mantle as the city’s highest-grossing adult film for over a decade.

Taking almost twice the time to shoot than conventional films and with a higher budget, more advanced equipment and elaborate lighting, the takeup of 3-D productions has been relatively slow in the porno industry despite early excitement at its promise.

“We have to change the lenses for a long time, the setting, lighting, we need more time than a normal movie,” said Japanese porn star Saori Hara after completing a scene.

Despite this, other major 3-D sex flicks are now reportedly in the works. Adult entertainment firm Hustler is reportedly working on a three-dimensional porno-spoof of the lithe, blue aliens in “Avatar,” while Italian director Tinto Brass plans to film a 3-D version of his classic 1979 erotic film “Caligula,” based loosely on the dissolute life of the Roman emperor.

The Hong Kong film has attracted the attention of distributors across Asia and Europe.

“The sex scenes are explicit and sometimes violent, but the main theme of the story is love,” said Sun, the director.