Christopher Nolan’s Oppenheimer is so intense that some viewers needed to 'leave the movie' to 'emotionally' recover.

The film will be the director's first ever biographical drama and will follow J. Robert Oppenheimer in devising the atomic bomb during WWII.

Peaky Blinders' Cillian Murphy plays the theoretical physicist, joined alongside Robert Downey Jr., Matt Damon and Emily Blunt.

Universal Pictures

The film itself has promised to be a nuclear hit after Nolan, 52, opened up on the challenges of showing an atomic explosion without resorting to computer-generated imagery (CGI).

In an interview with Games Radar's Total Film, he said: "I think recreating the Trinity test [the first nuclear weapon detonation, in New Mexico] without the use of computer graphics, was a huge challenge to take on.

"It’s a story of immense scope and scale. And one of the most challenging projects I’ve ever taken on in terms of the scale of it, and in terms of encountering the breadth of Oppenheimer’s story."

Universal Pictures

Ahead of the film's cinema release on 21 July, Nolan said people have been walking out of the screenings feeling absolutely 'devastated'.

"Some people leave the movie absolutely devastated," he told Wired. "They can’t speak. I mean, there’s an element of fear that’s there in the history and there in the underpinnings.

"But the love of the characters, the love of the relationships, is as strong as I’ve ever done."

He added: "It is an intense experience, because it’s an intense story. I showed it to a filmmaker recently who said it’s kind of a horror movie. I don’t disagree."

The filmmaker - who wants the movie to be of 'immense scope and scale' - has also explained why Oppenheimer switches from colour to black-and-white.

ABC

Nolan said: "I wrote the script in the first person, which I'd never done before.

"I don't know if anyone has ever done that, or if that's a thing people do or not.

"The film is objective and subjective."

He then explained that 'the colour scenes are subjective' and 'the black-and-white scenes are objective', adding: "I wrote the colour scenes from the first person.

"So for an actor reading that, in some ways, I think it'd be quite daunting."

The film will be Nolan's first R-rated movie in 21 years.

The official synopsis reads: "J. Robert Oppenheimer is one of the iconic figures of the twentieth century, a brilliant physicist who led the effort to build the atomic bomb for his country in a time of war, and who later found himself confronting the moral consequences of scientific progress."