James Cameron's top-secret 3-D epic sci-fi movie Avatar is suddenly not so secret: On Tuesday, he screened about 24 minutes of it at the Cinema Expo in Amsterdam.

You can read a blow-by-blow description of the footage over at ComingSoon.net, and The Hollywood Reporter also has an account of the presentation:

The fittingly epic film promo literally added an extra dimension to Fox's presentation at the ongoing Cinema Expo.

Avatar actors Sam Worthington, Sigourney Weaver, Zoe Saldana and Stephen Lang, pic producer Jon Landau, and Fox film chairman Jim Gianopulos also greeted the clearly wowed exhibs at the RAI convention center auditorium.

"Three years ago, I stood up here and said the 3-D renaissance is coming," Cameron said. "And from what we've seen in the business, we can now say it has arrived."

In introducing the 24-minute assemblage, Cameron said much of it came from the first third of the film but that there were also glimpses from unfinished portions of later battle scenes involving warring sides clashing over control of the fantasy world Pandora.

We're eager to see the movie, which rumor says will be featured in a panel and possible screening of some of the footage at Comic-Con next month. We're told that Cameron's even trying to get Hall H at the San Diego Convention Center tricked out for 3-D projection, but we'll see about that.

Avatar opens Dec. 18.