Fans of James Cameron's Avatar will have to wait even longer to see a sequel after the director pushed the second film's release back by a year.

The Titanic moviemaker has been working on three follow-ups to the 2009 sci-fi epic, and had hoped to take the next installment to cinemas in 2016.

However, Cameron has now revealed the writing process is taking longer than expected, so fans will have to wait until 2017 for the first follow-up.

He says, "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 stand-alone film... We're writing three simultaneously... And parallel with that, we're doing all the design. So we've designed all the creatures and the environments."

Avatar won three Oscars and became the highest-grossing film ever with worldwide box office takings of almost $3 billion.

More: James Cameron Announces That First Avatar Sequel Has Been ...

The Hollywood Reporter: James Cameron Says 'Avatar' Sequel Delayed Until 2017 - The ...