Stephen Frears' "Philomena" took the Venice film festival by storm on Saturday, hailed as a frontrunner for the Golden Lion award with its tragi-comic tale of a mother's search for her son.

The British film, starring Judi Dench as mother Philomena Lee and comic actor Steve Coogan as the ex-BBC journalist who helps her in her quest, drew laughs, tears and rounds of spontaneous applause.

"Philomena" debuted at the Venice film festival alongside James Franco's "Child of God", the chilling tale of a cave-dwelling necrophiliac, and "Night Moves" about three eco-warriors who plot to blow up a dam.

Asked why he had made a film about such a taboo subject, Franco said it had provided a way "for me to examine something that's pushed out of civilized society".

Frears, director of the award-winning "The Queen", was set to take to the red carpet along with Dench and Coogan later Saturday.

Based on the true story recounted in Martin Sixsmith's 2009 book "The Lost Child of Philomena Lee", the film tells the tale of a teenage girl who falls pregnant in Ireland in 1952 and is packed off to a convent.

Her baby son is given up for adoption and all trace of him is lost.

Ex-journalist Sixsmith, at a loose end after being sacked from his role as a government spin doctor, decides to help, sparking an unlikely alliance between an Oxbridge wise-cracker and a feisty Irish pensioner.

Dench, known by many for her role as the head of the British secret intelligence service "M" in the James Bond films, gives a compelling performance of a woman grappling with love, loss and her Roman Catholic faith.

Coogan, who worked on the screenplay with Jeff Pope, captures a delicate balance between irony and compassion, ribbing the Church and expressing all the outrage against the "evil" nuns that Philomena herself is unable to feel.

"I really liked the British humor which contrasts with the religious issues," said Jacopo Mascholini, a 22-year-old student from Rome who attended the screening.

Frears said the real Philomena visited the set during shooting and described her as "a magnificent woman with no self-pity, who... despite all the injustices she has suffered still retains her religious faith".

OUTSIDERS COME IN

The two other films being premiered on Saturday and entering the running for a prestigious Golden Lion award depict characters isolated from society.

Kelly Reichardt's "Night Moves" stars Jesse Eisenberg alongside Dakota Fanning and Peter Saarsgard as young radical environmentalists who plot to destroy a huge dam.

Eisenberg's Josh lives in an environmentally sustainable commune, surrounded by organic artichokes and aura-reading machines, without any obvious family of his own, and fails to fit in.

"He is an outsider of the outside," Reichardt told Reuters on Saturday. "But Josh feels pretty right about everything, so that's his sort of impetus."

Texas-born actor Scott Haze plays a lonely Tennessee backwoodsman whose traumatic life twists him into a necrophiliac and murderer in "Child of God", based on Cormac McCarthy's novella of the same name.

Director Franco plays a bit part in the film, which requires English subtitles to decode the grunting delivery of Haze's character Lester Ballard.

"It was a way for me to examine something that's pushed out of civilized society, and someone who is extremely isolated and lonely and who wants to in fact connect with other people but is in fact incapable," Franco said after the film's premiere.

Nick James, editor of the British film magazine Sight & Sound, was not convinced the film had pulling power.

"I'm not sure why anyone would want to see it who is not a James Franco fan," he said.