This terrifying new horror film is so scary it's leaving viewers feeling violently ill and unable to sleep ...

WARNING: this is not for the faint-hearted.

If you're a big horror film fan, then there's a big chance you've heard of Midsommar by now. 

The new movie has built up a reputation as being a thrilling masterpiece that has left some audience members feeling violently ill and unable to sleep.

Set during a nine-day pagan festival in Sweden, Midsommar has earned several five-star reviews from critics, including The Telegraph's Tim Robey, who called it "heroically upsetting".

"Sick but also beautiful, the film gets away with an impressively audacious running time, simply because it can. It dazzles you with dread," writes Robey.

Even the film's stars were traumatised by the final cut, with actor Will Poulter telling Vulture: "I was so f***ed up after watching it that I didn't sleep. It's maybe the most aggressive reaction I've ever had to a film."

The film follows the story of an American couple on the rocks who decide to join a group of friends on a trip to a midsummer festival in an isolated Swedish village.

However, the film takes a sinister turn as the villagers involve the visitors in increasingly disturbing rituals.

Midsommar will be in New Zealand cinemas from August 8.