"Great Gatsby" actress Carey Mulligan traded in her Tiffany jewellery and Prada-designed flapper dresses for polo necks and duffel coats in her second star turn at the Cannes Film Festival Sunday in the Coen brothers' eagerly anticipated "Inside Llewyn Davis".

Mulligan stars with Justin Timberlake and Oscar Isaac as folk singers chasing fame and success in early 1960s New York in a bleakly comic film greeted by one critic as the "best so far at Cannes" while another hailed a "stupendous soundtrack".

Mulligan transforms herself into dowdy ratbag Jean, who has just discovered she is expecting. "Where were we?" Llewyn asks a furious Jean after he interrupts yet another of her tirades to chase down a street after a cat he has lost.

"You were calling me a careerist and I was calling you a loser," she tells him to laughs from the Cannes audience before he sets off on a trying road journey to Chicago in search of work.

In another scene, Llewyn sings his heart out under the stony gaze of a hard-bitten club owner. As his career dreams slip away, his would-be employer tells him flatly: "I don't see a lot of money here."

Guatemalan-born US actor Isaac as Llewyn sang and played guitar live on set for the film, the Coen brothers' first movie in competition for the Palme d'Or since "No Country for Old Men" in 2007.

The film was met with warm applause at a press preview on Saturday.

"What an intense pleasure this film is, one of the Coens' best, and the best so far at Cannes," said the Guardian.

"Above all 'Inside Llewyn Davis' is a revelatory showcase for Isaac, who sings with an angelic voice and turns a potentially unlikable character into a consistently relatable, unmistakably human presence," said US entertainment trade magazine Variety.

The Hollywood Reporter praised a "gorgeously made character study leavened with surrealistic dimensions both comic and dark".

The latest offering from brothers Joel and Ethan was as "stunning and singular as anything in the Coens' canon", it added.

Joel Coen won the Palme d'Or in 1991 for "Barton Fink", and the brothers have made frequent trips to the French Riviera festival with other films selected for the invitation-only competition.

"Inside Llewyn Davis" is Mulligan's second Cannes outing this year after her performance as Daisy in Baz Luhrmann's "The Great Gatsby", which opened the festival on Wednesday.

The 27-year-old British actress, who as a teenager ignored advice to forget acting and "marry a banker", came to the attention of Hollywood after a critically acclaimed debut on Broadway in Chekhov's "The Seagull".

She went on to win a best actress Oscar nomination before she was 25 and has since starred in a string of Hollywood movies including "Drive" with Ryan Gosling.