Sam Worthington says filming underwater scenes without oxygen for Avatar sequel was the hardest thing he's EVER had to do as an actor

Sam Worthington has revealed that filming the sequel to the blockbuster Avatar was the 'hardest thing' he's ever had to do.

The former bricklayer, 46, says he had to learn to 'free dive' -deep water diving without scuba gear- for his role in Avatar: The Way of Water.

In the blockbuster, Sam returns as Jake Sully. He lives on the alien moon Pandora and shares four kids with Na'vi warrior Neytri (played by Zoe Saldaña).

Sam Worthington has revealed that filming the sequel to the blockbuster Avatar was the 'hardest thing' he's ever had to do. Pictured with wife Lara Worthington in 2022

Sam Worthington has revealed that filming the sequel to the blockbuster Avatar was the 'hardest thing' he's ever had to do. Pictured with wife Lara Worthington in 2022 

Sam described his intense feelings about trying to act underwater in the movie, which reputedly is amongst the most expensive ever made.

'There's a very emotional scene between me and [my son in the film],' he told News.

'But we are thirty feet underwater and running out of oxygen. You've got to forget to forget that you're deep down, that you're depleting all your oxygen, and just play this emotional scene between a father and a son.'

The Terminator star described the experience of making the film, directed by Titanic hitmaker James Cameron, as 'daunting'.

Sam told the publication that he took many months to learn how to free dive, and was taught by the world's best.

The former bricklayer, 46, says he had to learn to 'free dive' - deep water diving without scuba gear - for his role in Avatar: The Way of Water

The former bricklayer, 46, says he had to learn to 'free dive' - deep water diving without scuba gear - for his role in Avatar: The Way of Water 

He became skilled at slowing his heart rate and learned 'how to get more oxygen into your bloodstream.'

But once he had the skills to survive under water without oxygen for long periods, the hard part, he says, was 'getting rid of it', when it came time to film the emotional scenes.

Many cast members -including Kate Winslet and Sigourney Weaver- were trained to free-dive for over six minutes at at time inside a 900,000-gallon tank in Manhattan Beach, CA.

Zoe Saldana and Sam Worthington in the 2009 mega-hit Avatar

Zoe Saldana and Sam Worthington in the 2009 mega-hit Avatar 

Like Avatar, The Way of Water was filmed using a motion capture, where actors movements are recorded and used as the basis for an animation process.

Much of the estimated $250million (AUD$370m) is set in and around the ocean of reef-dwelling Na'vi called the Metkayina lead by Tonowari played by Kiwi-actor Cliff Curtis. 

The original Avatar is one of the highest grossing movies of all time, pulling in around US$2.9billion at the box office worldwide. 

Around $785million of that was made in the US. The third highest grossing movie of all time is Cameron's own Titanic, which made $2.1 billion when it was released in 1997, around US$3.8 billion in today's money. 

In Australia, Avatar is the most successful film ever released here, grossing $115,781,489.

Avatar: The Way of Water will be released in cinemas on December 15 

Avatar: The Way of Water cost a reported US$250million

Avatar: The Way of Water cost a reported US$250million