Movie-goers flocked to see what is billed as the world's first 3D porn film as it opened to packed cinemas across Hong Kong on Thursday, with some screenings selling out completely.

Loosely based on a piece of classical Chinese erotic literature, the $3.2-million Cantonese-language movie '3-D Sex and Zen: Extreme Ecstasy' features orgies, swinging and some very graphic sex scenes.

Curious movie-goers from all walks of life - office workers, retirees and students - formed long queues outside cinemas in the southern Chinese city, eager to catch an eyeful of steamy 3D action.

Many in the crowd were women and were not shy about watching the movie.

"I'm not normally much of a movie-goer, but this one is just too good to miss," 32-year-old Justin Lai told AFP as she waited at a cinema in Causeway Bay, one of the city's busiest entertainment districts.

"I'd like to see what 3D porn is like on the big screen."

College student Yan Shek, 21, was also among the first to see the movie in a morning screening. The 113-minute film has been rated Category III in Hong Kong, which bars anyone under 18 from watching it.

"We are very curious," she said.

"It is the first time to see an X-rated film in the cinema. It should be very interesting."

Another movie-goer said he snuck out of work to watch the movie.

"I'm catching the first show on the first day so I'll be the first of my friends to see it," said sales executive David, who declined to be identified in full.

Set in the Ming dynasty, the film chronicles the story of a young man who, after being introduced to the erotic world of an aristocrat, realises his ex-wife is the love of his life.

The film stars Japanese adult actresses Yukiko Suo and Saori Hara.

The movie will open in Taiwan on Friday and has sparked strong interest in many Asian markets, including Japan and South Korea, as well Europe and the United States, according to the producer.

Travel operators were reportedly organising moviegoing excursions to Hong Kong and Taiwan for tourists from mainland China, where strict censorship rules prevent any screening of the film.

"We are very pleased with ticket sales," Sharyn Yau, publicist for China 3D Digital Entertainment Ltd told AFP.

"Last week, we heard that 70-80 per cent for this weekend's tickets have already been sold. People obviously love the movie."

But South China Morning Post film critic Paul Fonoroff was left rather underwhelmed by the romp, describing it in a review as over-long, one-dimensional and short on real passion.

"Perhaps the most ironic element is the script's ostensible moral that sincere love is more satisfying than wanton promiscuity, a concept which, if truly put into practice, would cause ticket sales to go flaccid," he wrote.

The movie is a remake of the 1991 film 'Sex and Zen', which is still the highest-grossing Hong Kong adult movie of all time.

"3-D Sex and Zen: Extreme Ecstasy" opens ahead of reported plans by other filmmakers to produce similar 3D porn movies.

Italian director Tinto Brass has announced he is to produce a 3D remake of his 1979 erotic film Caligula, while Hustler plans to release a pornographic spoof of 3D science fiction film Avatar, the top-grossing movie of all time.