'Avatar' sequel 'monumental', says Worthington

James Cameron's sequel to 'Avatar' will be "monumental", its lead actor Sam Worthington has claimed.

The director pioneered filming in 3D with the film, about the blue Na'vi - alien inhabitants of another planet – and Sam Worthington, who starred in the movie, says he is to try something even more adventurous for his next film, possibly setting it underwater.