A powerful lesbian love story starring Cate Blanchett and a groundbreaking Holocaust drama emerged as favourites as the Cannes Film Festival hit the halfway mark on Monday.

Critics are calling it a banner year at the world's top cinema showcase, with the selection of 19 contenders for the coveted Palme d'Or top prize filled with delights and surprises.

In an early stand-out, Todd Haynes's "Carol" features Blanchett as a wealthy 1950s housewife who falls hard for a budding photographer (Rooney Mara).

The lushly shot period piece sees Carol, in the process of divorcing her businessman husband, threatened with the loss of custody of her young daughter on "moral grounds".

The film makes a strong case for equal rights at a time when, as Blanchett noted after the screening, dozens of countries still have anti-homosexuality laws on the books.

Rapturous reviewers in this Riviera port town said "Carol" had already emerged as an Oscar favourite.

Film industry bible Variety called it "an exquisitely drawn, deeply felt love story that teases out every shadow and nuance of its characters' inner lives".

The unflinching Holocaust feature "Son of Saul" by Hungarian newcomer Laszlo Nemes also drew rave reviews from shocked critics.

Cannes watchers said the unique relentlessness of Nemes's depiction of a 36-hour period in the Auschwitz death camp could win over the jury led by US filmmakers Joel and Ethan Coen.

French daily Le Monde said Nemes, who lost several members of his family to the gas chambers, said he clearly made the film to keep the history of the Holocaust alive for "the generations that soon will have no direct contact with the witnesses who can share with them their memories".

Among the more bizarre entries, which nevertheless won ardent fans, was "The Lobster" by Greek director Yorgos Lanthimos starring Colin Farrell and Rachel Weisz in a story about single people sequestered in a hotel and given 45 days to find a partner, or be transformed into the animal of their choosing.

- Potential gems -

The darkly comic send-up of modern love packed an emotional punch, with BBC critic Nicholas Barber giving it five out of five stars and calling it a "shrewd commentary on the societal pressures we're all under to form relationships, and the deceptions and self-deceptions some of us resort to as a result".

Italian veteran Nanni Moretti also drew high marks for his new picture, "My Mother".

Moretti stars alongside US actor John Turturro in a semi-autobiographical film about a director suffering personal and professional crises that left many Cannes critics weepy as they emerged from the giant Palais main venue.

Audiences also embraced Hirokazu Koreeda's "Our Little Sister", a gentle Japanese family drama adapted from manga, and the Italian-made, English-language "Tale of Tales," a bloody Gothic fable starring Salma Hayek and John C. Reilly.

But in one of the biggest Cannes flops in recent memory, Gus Van Sant garnered howls for "The Sea of Trees" starring Oscar winner Matthew McConaughey as a man who travels to Japan to commit suicide.

London's The Guardian newspaper called it a "fantastically annoying and dishonest tear-jerker".

Always a potpourri of high art and big-money commercial fare, the festival also saw the rip-roaring premiere of a new "Mad Max" blockbuster starring Charlize Theron and Tom Hardy.

Scott Roxborough of trade magazine The Hollywood Reporter told AFP that the second half of the festival still had many potential gems in store.

He said "Youth" by Oscar-winning Italian director Paolo Sorrentino with Michael Caine, Weisz and Jane Fonda; "Dheepan," a drama about a Sri Lankan refugee by acclaimed French director Jacques Audiard; and Chinese director Jia Zhangke's follow-up to his 2013 tour de force "A Touch of Sin" looked particularly intriguing.

Roxborough said the Cannes market, where film rights are bought and sold, was also bouncing back after a few lean years.

"It's not up to the levels before the crash of 2007-2008 when people were going crazy with $100-million films flying around like candy," he said.

"But people haven't been buying for a couple of years so they're restarting the market. And of course a lot of territories' economies are doing a bit better" including Spain, Italy and sanctions-hit Russia "which has sort of bottomed out now and is rebounding".

The 12-day festival will wrap up on Sunday with a gala awards ceremony.