New behind-the-scenes photos show Avatar stars in gruelling underwater shoot in New Zealand

Kate Winslet and Zoe Saldana star in the upcoming Avatar films. Photo / Twitter

Filming for the Avatar sequels may be on hold, but fans are in for a treat this week as 20th Century Fox has released new behind-the-scenes photos from the set.

The photos were taken earlier this year on location in New Zealand. Filming is on pause because of the coronavirus outbreak, but visual production work is still underway in Manhattan Beach, California, according to the Daily Mail.

With a combined budget of $500 million, Avatar 2 and 3 are being filmed at the same time. Avatar 2 is scheduled to hit theatres in December 2021, and the third movie is due for release in 2023.

The movies largely take place underwater, and most of the filming has been done in a huge 900,000-gallon tank of water.

The behind-the-scenes snaps show stars Kate Winslet, Zoe Saldana, Sam Worthington and Cliff Curtis floating in the tank during a filming break.

In the photo a layer of white balls can be seen, designed to keep studio lights from interfering with underwater filming.

The actors had to learn to hold their breath for several minutes. Photo / Twitter

Another photo shows director James Cameron perched on scaffolding above the tank as he directs the cast's movements.

Most of the cast learned to free dive for their roles and can hold their breath underwater for several minutes. Kate Winslet held her breath for nearly seven minutes during one underwater scene, producer Jon Landau told Cinema Blend last year.

"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.

James Cameron is directing the films, which were shot in New Zealand until the pandemic put a pause on filming. Photo / Twitter

"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!"

But it isn't just the adult actors who need to learn to hold their breath underwater.

Cameron told Collider last year that six teenagers and a 7-year-old cast member learned to hold their breath for up to four minutes at a time.