Christopher Nolan cut the filming of 'Oppenheimer' to 57 days to free up funds to build Los Alamos.

Production designer Ruth De Jong has revealed they were running out of money while she was designing the town in New Mexico, which is one of the development and creation places of the atomic bomb.

However, the director came up with a way to increase the set design budget by cutting back on the time they had to shoot the flick from 85 days to 57.

Speaking on the 'Team Deakins' podcast, Ruth spilled: “It felt like a $100 million indie.

“This is not 'Tenet' [which was shot in 96 days]. Chris wanted to shoot all over the United States…just plane tickets alone and putting crew up all over the place [is expensive]. Not to mention I have to build Los Alamos, it doesn’t exist. That’s where I really felt like it was impossible.”

She continued: “Chris said, ‘Forget the money. Let’s just design what we want.’ So that’s what we did, and when construction first budgeted my town it was $20 million. Chris was like, ‘Yeah, no. Stop.’ We had this huge white model and I started pulling buildings out of it, not to mention we want to shoot in New York and New Jersey and Berkeley and Los Angeles and New Mexico.”

Executive producer Tom Hayslip said at one point they'd have to cut Berkeley from the locations list, which is where Oppenheimer was a professor of physics.

Ruth told him: “But we have to go to Berkley. That is Oppenheimer!”

And Christopher decided to cut the filming time to free up some funds.

Ruth recalled: “The producers were asking what I could do on my end to shrink [the budget]. Tom then comes into my office and says, ‘Chris is going to shoot this in 55 days.’ That is a lot of money we get back.

“At that point, you feel like I have to deliver above and beyond because he just went and gave up his days. He, more than anyone, knows what he wants to get in every single day and how he wants to get it and he goes from 85 to 55 days.”

Cillian Murphy, who plays one of the masterminds behind the world's first atomic bomb, J. Robert Oppenheimer, previously shared how fast-paced filming was.

He told the 'WTF with Marc Maron' podcast: “We made the movie unbelievably quickly. We made it in 57 days. The pace of that was insane.

“The sets are huge, but it feels like being on an independent movie. There’s just Chris and the cameraman — one camera always, unless there’s some huge, huge set piece — and the boom op and that’s it. There’s no video village, there’s no monitors, nothing. He’s a very analog filmmaker.”