The film's plot sees a black family move into a predominantly white suburban community in the 1950s.

"The trickiest part [of shooting] was, we were in a very racially diverse neighbourhood in Fullerton, California," Clooney said.

"And we had about 350 extras who were going to hurl a lot of racial slurs and say a lot of pretty terrible things."

Clooney added: "Everybody who was making the film, we all just felt sick while we were doing it."

Referring to the way the family is treated in the film, the director said: "These are things that happened - [neighbours] sang church hymns, they hung confederate flags over the fence, they built a fence around their house, these are things that really happened.

"But it was sickening to be part of it quite honestly, so that was one of the most difficult things to shoot."

The movie, which is currently showing as part of the Toronto Film Festival, was conceived during the run up to the US election of November 2016, which was won by Donald Trump.

Clooney said: "We'd seen some things on the campaign trail where they were talking about building fences, and scapegoating Mexicans and Muslims, and we're always reminded that these aren't new things and new moments in our history.

"So we thought it would be interesting to talk about it, but we wanted the film to be entertaining, not a documentary, we didn't want it to be an eat-your-spinach piece of filmmaking.

"So we merged it with [an existing Coen Brothers script] Suburbicon, because we thought it was a funnier idea to put it in the suburbs in the 1950s where we all thought everything was perfect - if you were a white straight male."

The actor and director said the real-life political climate the film was shot in ultimately altered the tone of the movie.

"While we were shooting, Trump was elected, and it changed the temperature of the film in a weird way," Clooney explained.

"The country got angrier, whichever side you were on. We had to cut some of Josh Brolin's scenes out, and one of the reasons is they were really slapstick funny, and it felt like the wrong tone suddenly."

The film stars Matt Damon, Julianne Moore and Karimah Westbrook - who drew parallels between her character (the mother of the African-American family) and her own experience of the entertainment industry.

"I think early on there was a lot of correlations as far as what I've experienced in Hollywood," she said.

"I wore my hair natural for a very long time, so when I first moved to Hollywood I had an afro, and my manager said 'You'll never work with your hair like that, you'll have to straighten it'.

"I struggled with that for years, my looks, my hair... but I feel like things have changed so much in the industry, we have so many African-American women starring in shows now, so I feel there's been progress, but there's still a lot of things we're facing on both sides."