An epic lesbian love story with graphic sex, a Coen brothers musical comedy and a blood-stained critique of Chinese society rocked the 66th Cannes Film Festival but critics said no hands-down favourite had emerged ahead of Sunday's prizes.

After 20 films in competition in what reviewers said was a fairly strong year at the world's top cinema showcase, at least a quarter of the pictures looked like possible winners of the Palme d'Or top award.

A jury led by Steven Spielberg and packed with fellow Oscar winners Nicole Kidman, Ang Lee and Christoph Waltz among other luminaries was to deliberate in seclusion at a villa in the hills above Cannes.

Critics swooned over French-Tunisian director Abdellatif Kechiche's coming-of-age tale "Blue is the Warmest Colour" about a 15-year-old girl's first love, an older woman.

At three hours in length, the picture follows the arc of lead character Adele's (Adele Exarchopolous) tender passion for a beautiful blue-haired art student played by rising star Lea Seydoux, while also exploring themes such as class in France and women's careers.

"Sure to raise eyebrows with its show-stopping scenes of non-simulated female copulation, the film is actually much more than that: it's a passionate, poignantly handled love story," a Hollywood Reporter critic said.

"Remarkably, though, the explicit scenes never really feel pornographic, especially since the film isn't about titillation or arousal."

It topped critics polls in trade journals Screen International and Film Francais as well as London bookmakers' rankings.

But reviewers wondered whether the jury would shy away from rewarding its lengthy depictions of on-screen lovemaking -- among the most explicit in Cannes competition history.

Joel and Ethan Coen's "Inside Llewyn Davis" starring Carey Mulligan, Justin Timberlake and newcomer Oscar Isaac in the title role delighted audiences with a mix of soulful 1960s folk singing and absurdist humour.

The Coens won Cannes in 1991 with "Barton Fink" and last joined the competition in 2007 with "No Country for Old Men".

China's Jia Zhangke offered a shocking look at rampant corruption and exploitation of average citizens in his country that builds into a violent rage with "A Taste of Sin".

US website Salon called it "an art-house film with the body count of a 'Die Hard' sequel while London's Daily Telegraph said it depicted China as "cold and almost unnavigably vast; a place where sin may be the the only thing we have to keep us warm."

Iranian Oscar winner Asghar Farhadi made a strong showing early in the festival with "The Past" an intricately structured drama about a patchwork family set in France.

Other likely contenders included US director Alexander Payne's recession-era road movie "Nebraska" and lush Roman society portrait "The Great Beauty" by Paolo Sorrentino.

In a year in which gay themes resonated on and off screen, Steven Soderbergh's made-for-TV biopic of celebrity pianist Liberace and his long-time lover, "Behind the Candelabra", drew praise for its A-list stars Michael Douglas and Matt Damon.

A few films left audiences entirely cold, with loud booing and mass walkouts for the biggest disappointments.

Critics savaged one of the most highly anticipated entries, Danish filmmaker Nicolas Winding Refn's latest pairing with Canadian star Ryan Gosling after "Drive" captured the best director prize two years ago.

"Only God Forgives" set among the fight clubs of today's Bangkok served up an incessant onslaught of torture and gore, and reviewers hissed their disapproval as the credits rolled.

Japanese crime drama "Shield of Straw" by Takashi Miike about a nationwide bounty hunt for a child rapist who murders the granddaughter of a billionaire politician was dismissed as a "stone-cold dud" by one bored critic.

In the run-up to the main awards, a documentary by Cambodian-French director Rithy Panh about relatives wiped out in the Khmer Rouge's tyrannical grip on Cambodia in the 1970s picked up the prize in the "Un Certain Regard" category, which showcases films by emerging directors, late Saturday.

French drama "Amour" about an ageing Parisian couple took the Palme d'Or last year.