Venice (AFP) - A searing adaptation of one of most controversial books about the Holocaust divided critics at the Venice film festival Wednesday, with some fighting each other in the dark to get out of its first screening.

"The Painted Bird", based on Jerzy Kosinski's highly contentious 1965 novel about a Jewish boy surviving the worst human nature can inflict on him in an unnamed Eastern European country, was hailed as a masterpiece by some and an unwatchable ordeal by others.

But its staggering central performance from nine-year-old Czech Roma boy Petr Kotlar -- who witnesses a panoply of depravity from incest, bestiality and rape to mutilation and murder -- has had co-stars Harvey Keitel and Stellan Skarsgard as well as the critics in raptures.

That did not stop some running for the exits at its first screening.

In the very first scene, the boy's pet ferret is taken from him by boorish peasants and burned alive.

The Hollywood Reporter called the black-and-white epic "heart-wrenching... and the ideal film treatment" of the novel, which itself sparked outrage in Kosinski's native Poland when the writer first hinted that the story was autobiographical.

- 'Monumental work' -

The Guardian's Xan Brooks also heaped praise on Czech director Vaclav Marhoul for "never putting a foot wrong", adding: "One day they'll make a film about the first public screening" at Venice.

"It will feature the man who fell full-length on the steps in his effort to escape and the well-dressed woman who became so frantic to get out that she hit the stranger in the next seat," he wrote.

"The centrepiece will be the moment 12 viewers broke for the doors only to discover that the exit had been locked," he added.

Brooks declared the film "a monumental piece of work and one I'm deeply glad to have seen. I can also say I hope to never cross its path again."

Deborah Young of The Hollywood Reporter also hailed it, but warned that it was an "emotional three-hour punch in the stomach".

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Marhoul defended the unremitting darkness of his adaptation -- which has a happy ending, of sorts -- insisting that "only in darkness can we see light. Shining through all the horrors is, for me, hope and love."

He said the film was a warning of what can happen when Europe turns inward as it was doing now, drawing a parallel between the attitudes to migrant children fleeing wars in Syria, Libya and Afghanistan and the rejection and abuse his hero suffers.

- 'Kosinski lied' -

"Bad times are coming to Europe," he told reporters.

"Looking at the populists who are running so many European countries at the moment like Hungary, Poland, Russia, in the Czech Republic too and of course the US."

Marhoul said the film took 11 years to make.

"I didn't know when I started that this story would become much more accented by what happened in Europe three years ago, when so many people came here to save their lives," he said.

Because of the fury Kosinski sparked in Poland, the director decided to have most of the film's sparse dialogue in Slavic Esperanto "so no nation would be associated with villagers" who mistreat the boy and hand him over to the Nazis.

Despite being accused of plagiarising other Polish books, Kosinski's novel is still seen by many as a classic.

"When Kosinski said it was his autobiographical story he was lying," Marhoul said.

"In fact he spent the World War II with his parents among Polish villagers. And those villagers tried to save them... That's not a big problem for the book (because it is fiction). But many people in Poland still think this book is about them."