James Cameron's ambitious project to film three "Avatar" sequels at one time has proven so challenging that the three-time Oscar winner now expects to release the first follow-up in late 2017, one year later than originally anticipated,

"There's a layer of complexity in getting the story to work as a saga across three films that you don't get when you're making a standalone film," Cameron said as he helped promote New Zealand's local film industry in Wellington, according to The Hollywood Reporter.

The original target date for the first "Avatar" sequel was probably too ambitious, the director admitted, though he still hopes to have the scripts for all three movies completed by the end of January. Cameron is leading the writing team in charge of the screenplays.

"We're writing three simultaneously, and we've done that so that everything tracks throughout the three films," Cameron said. We're not just going to do one and then make up another one and another one after that."

The demanding visuals of the "Avatar" design, meanwhile, also take their toll, Cameron said.

"We've designed all the creatures and the environments," he explained.

The first "Avatar" movie, released in 2009, was praised for its groundbreaking visual effects. The film set in the mid-22nd century as humans mine a precious mineral on a lush, habitable moon, became the highest-grossing film in history with a box-office take of nearly $2.8 billion, according to the Chicago Sun-Times. The science-fiction saga also took home Academy Awards for best art direction, best cinematography and best visual effects.

Cameron plans to release his three sequels over consecutive years, reports USA Today. He wants each film to link to the next one, but also come to a resolution so that the audiences are not left with cliffhangers.

Following the recent hack targeting of Sony Pictures, meanwhile, the "Avatar" crew is taking greater security precautions to prevent leaks.

"I will only say (that is the case)," producer Jon Landau said, "but will not tell you how."