James Cameron has taken his time putting together the sequels to 2009's Avatar, but it seems work is finally getting underway. The ambitious director has big plans for the films, assembling a huge writing team and hoping to film the follow-ups in two back-to-back blocks.

The original film was a milestone for CGI in cinema and brought about the most recent boom in 3D filmgoing. Naturally, Cameron wants to push the envelope further this time around, using with glasses-free 3D projections.

New Zealand-based special effects studio Weta Digital will be a key part in the sequels, having been responsible for the original's groundbreaking computer imagery. They're back for Avatars 2, 3, 4 and 5.

"What Joe Letteri [senior visual effects supervisor] and Weta Digital bring to these stories is impossible to quantify," director James Cameron told Variety.

"Since we made Avatar, Weta continued to prove themselves as doing the best CG animation, the most human, the most alive, the most photo-realistic effects in the world. And of course, that now means I can push them to take it even further."

Letteri added: "Avatar is the ideal type of film for us. Jim's vision for the world of Pandora was always so much bigger than what we created for the first film.

"Helping him expand the language of cinema through new narratives set in such an expansive universe is the type of opportunity that rarely comes along twice. Projects like this allow everyone involved to push themselves to do their best work."

"The excitement at Weta around Avatar is obvious and the fact is that we have already been working on it for a number of years," said Weta Digital executive producer David Conley.

"During that period we have grown the company to a size and model that allows us to expand beyond any one project. This enables us to find a mix of other films that can help us grow along with Avatar, as is the case with Alita: Battle Angel, Avengers: Infinity War and Mortal Engines, to name a few of the other films we are currently working on."

Filming has yet to begin on the Avatar sequels, which is it believed will see the returns of Sam Worthington and Zoe Saldana in their roles as Jake Sully and Neytiri, a member of the alien race Sully joins when he inhabits the alien avatar bodies that give the film its title.

Sigourney Weaver is also expected to return, but other than that details are thin on the ground.

Avatar 2 is set to release on 18 December 2020, 11 years after the original, with Avatar 3 following a year later. These films will be shot back-to-back, with the next two filming consecutively at a later date before they're released in December 2024 and 2025.