SAN DIEGO (AFP) – Comic-Con kicked off with a chorus of shrieks – and litres of blood – as New Line Cinema unveiled spine-chilling footage from It: Chapter 2, a sequel to the highest-grossing horror movie of all time.

The Warner Bros-owned studio used Wednesday’s (July 17) preview night of the world’s largest pop culture fan gathering to showcase its concluding film of Stephen King’s 1986 novel about a terrifying clown who lurks in the sewers, preying on children’s most nightmarish fears.

The adaptation was split into two by director Andy Muschietti, with the first part released in 2017.

The sequel, out on Sept 6, stars Jessica Chastain and James McAvoy as grown-up versions of the haunted children returning to their creepy hometown 27 years later to battle Pennywise the clown.

Asked by host Conan O’Brien about a clip showing her character covered head-to-toe in blood, Chastain said she had volunteered for the full immersion – but later regretted it.

“I just was like, let’s make ‘Carrie’ on steroids,” she told a packed downtown theatre. “And that’s what he (Muschietti) did. And it literally tortured me through the whole movie.”

One haunting clip showed McAvoy’s character – an adult Ben Denbrough – racing through a claustrophobic house-of-mirrors in a bid to stop the clown’s murderous spree.

McAvoy said he pulled muscles and developed tendonitis during an arduous, physical shoot in which Muschietti demanded endless takes.

Zero Dark Thirty actress Chastain also praised the genre’s portrayal of strong women in the age of #MeToo.

“Right now, a lot of people are talking about female characters and arcs .

“I find that in horror films, they really honour women, in that women beat the monster at the end and usually the men die.”

The 50th anniversary edition of Comic-Con International brings 135,000 hyped-up devotees to a sweaty San Diego convention centre for the next four days, packed with glimpses of the next mega-hit films, TV shows – and a few comic books.