VENICE (AFP) ― Hollywood high-rollers George Clooney and Sandra Bullock kicked off the Venice film festival on Wednesday with a harrowing space drama that opens a line-up flush with gloomy tales.

“Gravity,” a 3-D sci-fi thriller, sees Clooney and Bullock as astronauts who are flung into deep space when a debris shower destroys their shuttle.

The stars sashayed down the red carpet to the song “Mambo Italiano” for the opening ceremony of the world’s oldest film festival, drawing wild screams from adoring fans who held up signs reading “We love you!”

Bullock, who stunned in a red, strapless, floor-length gown with a slit up the middle of the skirt to show off towering black heels, took photographs with devotees while a broadly-smiling Clooney in black tie signed hundreds of autographs.

The American actress, who wore her dark locks up, had reportedly spent a few days in Clooney’s villa in Lake Como before the festival.

Directed by Mexico’s Alfonso Cuaron of “Children of Men” fame, “Gravity” induces anxiety, with terrifying shots from inside the astronauts’ helmets as they spin wildly and lose all radio contact with Earth.

Cuaron has said he invented new filmmaking techniques to depict spacewalking ― including shooting inside a giant cube to evoke constantly shifting light sources ― and after months of delay and a huge budget, “Gravity” delivers a Hollywood punch.

Bullock plays Dr. Ryan Stone, a medical engineer on her first mission who relies on veteran astronaut Matt Kowalsky (Clooney) to hold on to her sanity and try to survive despite her rapidly dropping oxygen levels.

“It was the craziest, most bizarre, challenging shoot I’ve ever done,” Bullock told journalists, explaining how she had called astronauts on the International Space Station to get tips on how bodies move differently in space.

Clooney, dashing in a light grey suit, quipped that he had “done yoga and drunk my way into the part” and said the biggest challenge was learning how to “move slowly to mimic body movement in space, while speaking quickly.”

Director Cuaron said they had called in “advisors, scientists and physicists to teach the cast how things would react in space. A lot of the shots required the actors to be isolated, it was a very abstract way for them to perform.”

A soundtrack dominated by Stone’s racing heartbeat and the deafening silence of space is punctuated by jokes from Kowalsky: “Half of North America just lost its Facebook,” he cracks as debris takes out communication satellites.

While director of photography Emmanuel Lubezki produces stunning images which leave spectators gasping for air, the humour sometimes detracts from key scenes and there is little time before the accident for the characters to be developed in any real depth.

Festival director Alberto Barbera said he and other organisers had watched over 3,500 films before selecting the 53 which will be screened this edition.

“You will be disappointed in some cases and satisfied in others. Don’t expect a rollercoaster, but we have taken some calculated risks,” he promised.

Other keenly awaited premieres include “Parkland,” Peter Landesman’s re-creation of John F. Kennedy’s assassination and David Gordon Green’s brutal “Joe” with Nicholas Cage as a violent ex-con who teams up with a homeless teen.

Gondoliers could be seen shipping silver screen stars to Venice’s Lido island where the 70th edition of the festival will run to Sept. 7, accompanied by a plethora of luxury yacht parties and beach soirees.

Paparazzi were doused in sea spray as speed boats whipped past the shore of the Lido and starlets lounged in the Italian sun.

Scarlett Johansson, Nicholas Cage, Matt Damon and Zac Efron are just some of the stars expected on the red carpet this edition, along with South Korea’s Kim Ki-duk, whose grim morality tale “Pieta” won the Golden Lion prize last year.

Twenty films are up for the Lion this year.

The jury is headed up by Italian film director Bernardo Bertolucci, best known for his raunchy 1972 “Last Tango in Paris,” and includes British director Andrea Arnold (“Red Road”) and German actress Martina Gedeck (“The Lives of Others”).

British and American flicks dominate a line-up which reflects a “dark and violent reality” with filmmakers “not giving any signs of optimism,” Barbera said.

Thursday’s line-up features John Curran’s “Tracks” about a woman’s journey across the desert with only her dog and four camels for company, and Emma Dante’s “A Street in Palermo” which sees two women locked in a staring duel through their car windscreens.