The critically-acclaimed horror film Midsommar has been announced as a last-minute addition to the New Zealand International Film Festival line-up.

Midsommar is the second feature by Ari Aster, who directed Hereditary, lauded by many as the scariest film of 2018.

The Film Festival today announced that Midsommar has joined the line-up as a late addition, screening at Auckland's ASB Waterfront Theatre on August 4 and Wellington's Embassy Theatre on August 13.

Following American tourists whose trip to a Swedish pagan festival slowly descends into a nightmare, Midsommar has been praised as a "deeply upsetting," "wickedly funny," "psychedelic fairy tale".

Jack Reynor and Florence Pugh in Midsommar. Photo / AP
Jack Reynor and Florence Pugh in Midsommar. Photo / AP

Starring Florence Pugh, Jack Reynor and Will Poulter, Midsommar is reportedly so disturbing that even its stars had trouble sleeping afterwards.

"I was so f***ed up after watching it that I didn't sleep," said Poulter. "It's maybe the most aggressive reaction I've ever had to a film."

Following NZIFF, Midsommar is released in New Zealand on October 31.