Starring Denis Lavant as a man who adopts a dozen wildly different personas during the course of a long Paris day, the film includes surrealist scenes, tender moments, a song by pop star Kylie Minogue and the unexpected appearance of bonobo monkeys.
The film, which has its red-carpet gala on Wednesday, drew whoops and cheers at the end of its first press screening - but left other baffled viewers shaking their heads.
"This is what we have all come to Cannes for," said The Guardian newspaper's ecstatic five-star review. Screen International was less impressed, judging the film "a self-conscious upmarket weird-out."
"Holy Motors" is Carax' first feature since the experimental romance "Pola X," which screened at Cannes in 1999, to equally divided opinion. "Holy Motors" is one of 22 films competing for the festival's Palme d'Or.
It's a dramatic return - but don't ask Carax what he wants the public to take away from the film.
"I don't know. Who is the public? All I know is that it is a bunch of people who will be dead very soon," said the director, waving an unlit cigarette at a Cannes press conference. "I don't make public films, I make private films."
Minogue ventured that the film is about "how we present ourselves in the world in different moments."
It also brims with scenes that evoke other movies, from horror film "Eyes Without a Face" to "Blade Runner." Asked if it was partly a film about the history of cinema, Carax said: "Every film is."
Carax said he "conjured this (film) up out of my imagination" for Denis Lavant, who has been appearing in the director's films since the 1980s.
In "Holy Motors," Lavant portrays, among other characters, a beggar woman, a dying old man, a knife-wielding killer and a filthy gnome dragging a supermodel (Eva Mendes) through the city's sewers.
He said the hardest scene was the one in which his character interacts with the two monkeys.
"That was a bit scary," Lavant said. "Whoever you are acting with in a film, there are a lot of things that are unknown, but there's sort of an unacknowledged code. We share the same code of communication among human beings. When you're acting with a bonobo monkey it's much more difficult."
Minogue, who plays an old flame of Lavant's character - or one of his characters - said she had been "slightly terrified" to take an acting project very far from her performing start on shows like the Australian soap opera "Neighbours."
"It was overall a very beautiful experience," Minogue said.
"I banned my entire entourage from coming with me," she added. "I stripped myself of being Kylie and wanted to go being back to be as basic as possible and pretty much be a blank canvas for Leos."
