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.

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.