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Children waiting to watch Disney movie Frozen were shown explicit sex scenes when the trailer for Lars von Trier's x-rated Nymphomaniac was screened by mistake in a US cinema.

Parents in the audience were forced to distract and shield their children in a reportedly frantic effort to prevent a barrage of awkward questions.

"It seemed like forever when you're trying to, you know, cover a little guy's eyes," grandmother Lynn Green told Fox news. "I didn't have enough hands to cover his ears too and he got the sound down real good."

Those affected expressed concern about a lack of safeguards to stop similar errors happening in future. "You're talking, what, a PG-rated movie to all of a sudden have an R-rated scene up there for little children?" Green added.

The trailer for 'Nymphomaniac', was temporarily removed from YouTube. Photo: Zentropa/Trust Nordisk
The trailer for 'Nymphomaniac', was temporarily removed from YouTube. Photo: Zentropa/Trust Nordisk

Temporarily banned from YouTube for its overtly sexual content, the trailer shows Shia LaBeouf and Stacy Martin engaging in various sex acts amid a montage of often violent scenes.

Critics have called it one of the most explicit trailers ever to be shown in mainstream cinemas.

The Pinellas Park cinema in Florida has offered free tickets to those affected and apologised for the accidental screening.

Last year, a Nottingham cinema sparked an outcry after it began screening 15-rated horror movie Paranormal Activity 4 to children as young as five instead of the family animation Madagascar 3. The children at Cineworld were shown a bloodied corpse hurtling towards the camera during the first two minutes of the supposed Madagascar screening.

Disney's Frozen opened in US cinemas on Thanksgiving weekend, earning $93 million at the box office over the five-day holiday period. The film broke the record set by Harry Potter and the Philosopher's Stone in 2001 for the biggest Thanksgiving opening ever and also scored the largest for Walt Disney Studios.

Inspired by The Snow Queen fairytale, Frozen tells the story of a Scandinavian princess on a mission to find her sister, a queen who is unintentionally destroying their kingdom with the power to freeze anything she touches.

Nymphomaniac will debut in Copenhagen on Christmas Day before a likely general release in March in the UK next year.

The raunchy poster campaign, also directed by Danish Lars von Trier, shocked in October with its images of the cast pretending to reach sexual climax.

Uma Thurman and Jamie Bell are among the actors portraying orgasmic ecstasy to promote the film, which follows the erotic life of a woman from birth to the age of 50.

- Independent