It may boast ground-breaking 3D effects, but English-speaking viewers of "Avatar" have been left in the dark by the film's alien dialogue after Hong Kong cinemas offered only a Chinese translation.

The computer graphics-laden production by "Titanic" director James Cameron, which follows the exploits of a paraplegic army veteran in the alien world of the Na'vis, has raked in more than 2 million US dollars in Hong Kong since its release in mid-December.

Despite its box-office success, western movie-goers have complained Na'vi dialogue is utterly impenetrable -- unless they can read Chinese.

"While we both thoroughly enjoyed the film, we were somewhat disturbed and frustrated that the alien Na'vi dialogue only had Chinese subtitles," cinema-goer Nic Tinworth told the Sunday Morning Post.

Olivier De Molina told the Post that although the dialogue was not integral to the story, it "would have been nice to get everything. I just assumed that everything in Hong Kong is in both English and Chinese."

The local distributor of the movie, 20th Century Fox Hong Kong, refused to explain why no English subtitles were provided in some cinemas, the Post said.

The company's spokesman told the newspaper that they were "processing" the issue.

He added English subtitles for the movie were provided in eight local cinemas, although seven of them only showed its 2-D version, the report said.

Chinese and English are the official languages of Hong Kong, a former British colony that was returned to China in 1997. The city's cinemas normally provide subtitles in both Chinese and English if a movie is produced in a third language.

The 300-million-dollar "Avatar" was Cameron's first project with fellow Hollywood producer Jon Landau since the pair scooped 11 Oscars with "Titanic" in 1998.