PICTURED: Behind the scenes of Avatar sequels where Kate Winslet reunites with Titanic director James Cameron trained to 'hold her breath for nearly seven minutes underwater' after cast had to learn to free dive for grueling scenes in 900,000-gallon tank (11 Pics)

20th Century Fox have released new behind-the-scenes photos from the set of the Avatar sequels. 

The pictures, posted Friday to the official Avatar Twitter account, were taken earlier this year on set in New Zealand. Filming for the sequels is currently on hold due to the coronavirus outbreak, although visual production work is still continuing in Manhattan Beach, California. 

Avatar 2 and 3 are being filmed at the same time and have a combined budget of $500 million. Despite the COVID-19 outbreak, Avatar 2 is still scheduled to hit cinemas in December 2021.  The third film is due for release in 2023.   

The movies will largely be set underwater, and much of the filming has taken place in a gigantic 900,000-gallon water tank. 

One new behind-the-scenes snap shows stars Sam Worthington, Kate Winslet, Zoe Saldana and Cliff Curtis floating in the tank during a break from filming in New Zealand.

The cast are expected to swim and dive beneath the surface as camera crews capture their performance. 

20th Century Fox have released new behind-the-scenes photos from the set of the Avatar sequels. In this picture, Sam Worthington, Kate Winslet, Zoe Saldana and Cliff Curtis are seen floating in a tank during a break from filming in New Zealand

A second snap shows director James Cameron above the tank as he directs the cast on their movements

The movies will largely be set underwater, and much of the filming has taken place in a gigantic 900,000 gallon tank. Cameron is pictured directing his cast on a crane suspended above the tank 

The snap also shows a layer of white balls on the water's surface, designed to prevent studio lights from interfering with filming underwater. 

A second snap shows director James Cameron sitting on scaffolding above the tank as he directs the cast on their movements. 

Most of the actors learned to free dive for their roles, and can hold their breaths underwater for minutes at a time.  

Producer Jon Landau told Cinema Blend last year that Winslet held her breath for almost seven minutes during one grueling underwater scene. 

'Kate Winslet had to train in this and she got up to a static breath hold of just about seven minutes. It's amazing, it's mind over matter. You see Kate going underwater and she just felt so comfortable. 

'There was one day, we have a tank where she was just rehearsing and testing and we have some windows into it, and I go in there and she's just walking on the bottom [of the tank] left and right, left and right, left and right, then she sees me in the window and she just waves. I couldn't believe it!'

However, it's not just the adult stars who need to hold their breath underwater to act out their parts.  

Last year, Cameron told Collider that six teenagers and a seven-year-old cast member also learned to hold their breaths for up to four minutes at a time.   

Production on the $500 million movies has been taking place in New Zealand. The coronavirus outbreak has currently halted filming 

An aerial photo shows the full extent of the gigantic set. In addition to filming in New Zealand, dozens of professionals are also working on visual production work in California 

Dozens of crew members are seen inside the huge warehouse in New Zealand during filming last year. Avatar 2 and 3 are being made concurrently, but will be released two years apart 

Star Sigourney Weaver is pictured with producer Jon Landau (left) and co-star Joel David Moore (right) last year. The cast and crew will return to New Zealand to recommence filming in the near future 

'We've done a tremendous amount of testing. We've got six teenagers and one seven-year-old, and they're all playing a scene underwater. We've been training them for six months now, with how to hold their breath, and they're all up in the two-to-four-minute range,' he explained. 

'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.'

Meanwhile, other photos from the set - taken in 2019 - show dozens of crew watching the scenes back on computers set up inside the New Zealand warehouse.  

Avatar became the highest-grossing movie of all time after its release in December 2009, taking the title from another of Cameron's films, 1997's Titanic.

It was a record Avatar held for a decade until this year's Avengers: Endgame. 

Back in January, Cameron thrilled fans when he released concept art that inspired the two sequels 

The computer-generated images depict different locales within the lush world of Pandora that will appear in the two films. 

The cast and crew have been filming in New Zealand since 2018. However, production was shut down amidst the coronavirus outbreak two months ago. 

Cameron told Empire earlier this week that the country's swift response to the pandemic means filming could resume in the very near future. 

'On the bright side, New Zealand seems to have been very effective in controlling the virus and their goal is not mitigation, but eradication, which they believe that they can do with aggressive contact tracing and testing,' the director said.

'So there's a very good chance that our shoot might be delayed a couple of months, but we can still do it. So that's good news,' he added. 

Back in January, Cameron thrilled fans when he released concept art that inspired the two sequels. 

The four separate computer-generated images depict different locales within the lush world of Pandora that will appear in the two films. 

Meanwhile, there are also plans to make Avatar 4 and Avatar 5 - although shooting on those two movies has not yet sarted. The are anticipated for release in the late 2020s.  

Most of the images showed several large moons visible in the planet's sky

Producer Landau provided this update at the start of the COVID-19 outbreak