WATCH: Makers share spine-chilling footage from 'It' sequel

San Diego Comic-Con kicked off with a chorus of shrieks — and gallons of blood — as New Line Cinema unveiled spine-chilling footage from “It: Chapter 2,” the sequel to the highest-grossing horror movie of all time.

The Warner Bros-owned studio used Wednesday’s 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 — the first part, released in 2017, took a stunning $700 million at the global box office.

The sequel, out September 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 theater. “And that’s what he (Muschietti) did. And it literally tortured me through the whole movie.”

Chastain claimed that a world-record 4,500 gallons of fake blood were used in the production — all of which had to be kept freezing-cold to stop it fermenting in the summer heat.

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 multiple 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 honor 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 center for the next four days, packed with glimpses of the next mega-hit films, TV shows — and a few comic books.

Elsewhere on Wednesday, there was a screening for The CW’s upcoming “Batwoman” series, featuring Ruby Rose as an openly lesbian, feminist superheroine.

The show’s groundbreaking protagonist has already stirred controversy in some of the internet’s darker depths, but the early glimpse drew praise.

“Ruby Rose is fun as hell. Pilot is an origin story. And it is SPECTACULARLY gay!” tweeted SyFyWire journalist Jacob Oller.

Much-anticipated panels later in the week include a “Terminator” sequel reuniting Arnold Schwarzenegger and Linda Hamilton, a “Star Trek” showcase welcoming back Patrick Stewart, and a “Game of Thrones” reunion.

Marvel Studios is also expected to lift the lid on the next set of films in its hyper-successful “cinematic universe” of superhero movies.