The world's oldest film festival opens with Gravity, a 3-D sci-fi thriller starring George Clooney and Sandra Bullock as astronauts who are flung into deep space when a debris shower destroys their shuttle.
Other premieres are 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.
"This festival draws its strength from the risks it takes," this year's jury president, Oscar-winning Italian director Bernardo Bertolucci, said at a canalside cocktail party on the eve of the opening ceremony.
Gondoliers could be seen shipping silver screen stars to Venice's Lido island where the 70th edition of the festival will run to September 7th, 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.
Alongside Clooney, Bullock and Cage, red carpet stars will include Scarlett Johansson, Matt Damon, Zac Efron and 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 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, with the return of the family as the vessel for social, political and economic crisis, from child abuse and abductions to absent fathers and marriage breakdowns.
The total 53 films screening reflect a "dark and violent reality" with filmmakers "not giving any signs of optimism", festival director Alberto Barbera said.
Among the most harrowing will be James Franco's Child of God, an adaptation of a Cormac McCarthy novel about a cave dweller who rejects the social order and ends up slaughtering women to have sex with their corpses.
The squeamish will also be tested by Jonathan Glazer's Under the Skin, in which Johansson stars as an alien who hunts down and devours unwitting hikers.
Monty Python star Terry Gilliam's drama The Zero Theorem is unlikely to lift the mood, with its bleak tale of solitude and madness centred around a race to decode a mathematical formula to discover whether life has any meaning.
For the first time, two documentaries will also be running for the top prize: American Errol Morris's The Unknown Known: The Life and Times of Donald Rumsfeld and Italian Gianfranco Rosi's Sacro GRA about Rome's ring road.
"We've learnt that the distinction between fiction and documentaries belongs to the past, modern cinema moves constantly between the two," Barbera said.
Japanese animation master Hayao Miyazaki is also in the running with The Wind Rises, a World War II story adapted from Miyazaki's own manga.
Taipei-based director Tsai Ming-liang brings the only Chinese-language work to the competition with Stray Dogs about a family living on the margins.
Italian theatre-director Emma Dante is competing for the Lion with a debut, A Street in Palermo. A tale about a female feud in Sicily, it is also one of nine films vying for the Queer Lion award.