Hollywood high-rollers George Clooney and Sandra Bullock kicked off the Venice film festival on Wednesday, August 28 with a harrowing space drama that opens a line-up flush with gloomy tales, AFP said.

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

The stars were expected on the red carpet for the opening ceremony of the world's oldest film festival, followed by an exclusive after-dinner party.

Directed by Mexico's Alfonso Cuaron of "Children of Men" fame, the film 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.

While director of photography Emmanuel Lubezki produces stunning images which leave spectators gasping for air, the humour sometimes detracts from key scenes and the characters lack real depth.

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.