James Cameron says he has only just managed to shoot his first successful scene for Avatar 2, which is set underwater. 

The highly anticipated sequel to the Oscar-winning 2009 fantasy film has already had its release date pushed back several times due to the challenges of shooting motion capture underwater. 

Now, the 63-year-old director says that successfully shooting a full scene underwater was only achieved last week.

"We've done a tremendous amount of testing, and we did it successfully, for the first time, just last Tuesday (November 14). We actually played an entire scene underwater with our young cast." The cast includes six teenagers and one seven-year-old, who have been training for six months now to hold their breath, and the director says they're all up to the two to four minute range. "They're all perfectly capable of acting underwater, very calmly, while holding their breath. We're not doing any of this on scuba. And we're getting really good data, beautiful character motion and great facial performance capture. We've basically cracked the code," he adds. 

Earlier in 2017, the production was forced to announce it would not be completed in time for its previous release date of December 21, 2018. The Titanic director has revealed he doesn't expect to finish test stages until January 2018.

"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," he says.