James Cameron admits his 'Avatar' sequels need to be successful due to the budget he has spent.

The Academy Award-winning director helmed the hugely successful original sci-fi movie in 2009, but ahead of the release of the second installment in 2020, James admitted that the success of the initial upcoming film will determine whether the scheduled fourth and fifth movies will reach cinema screens.

Speaking at the Television Critics Association, Cameron said: ''I don't think you advance storytelling, you know. I mean, I think storytelling is always about the basics. It's about people. And I think that the lesson for me from the first film that I've applied to the new films is that the more fantastic the imagery, the more other-worldly, and the more you are pushing out to the edge of what's possible in terms of bringing imaginative imagery to the screen, the more it has to be grounded in relationship and in truth and in heart. And so I'm hopefully doing that in spades with the new films. I've got an incredible cast ... I've worked very hard to cast this, to find some new, young actors coming up that have incredible heart and that are just amazing. And, you know, it doesn't matter how much you dress it up with great production design and great visual effects. If the story is not working, if you don't connect to the characters, it's just simply not going to work. Of course, we can't afford for it not to work, the budget level that we are dealing with. But, of course, you always have to give yourself permission as an artist to fail no matter what the stakes are. You've got to try stuff. The least safe thing you can do is try to be safe.''

Last year the production was forced to announce it would not be completed in time for its previous release date of December 21, 2018.

And the 'Titanic' director has revealed he doesn't expect to finish test stages until January 2018.

He said: ''Now, we're still working in our small test tank. We graduate to our big tank in January. There's a tremendous amount of water work across 'Avatar 2' and 3. It's ongoing into 4 and 5, but the emphasis is on 2 and 3.''