On paper, it looked enticing: a high-stakes drama of love and loss by Gus Van Sant starring Oscar winner Matthew McConaughey and Naomi Watts and mostly set in Japan.

But "The Sea of Trees", premiering Saturday in competition for the Palme d'Or at the Cannes Film Festival, landed with a thud at its press previews, garnering the first big boos of this year's edition.

The picture, also featuring Japanese actor Ken Watanabe, drew unintended laughs and derisive whistles from the Cannes crowd, never shy about audibly expressing its views.

Critics later called it "long-winded", "sticky and gooey" and culturally patronising.

French film magazine Premiere pronounced it "without a doubt the worst film by Gus Van Sant", "an awful melodrama made of pure sugar" and simply "interminable".

McConaughey's career has been flying high since he bagged an Academy Award last year for "Dallas Buyers Club" and critical adulation for his role in the television series "True Detective".

But his turn as Arthur, a bespectacled American mathematician who travels to Japan to commit suicide, looks to have been a career misstep.

In the film, Arthur performs a Google search looking for "the perfect place to die" and ends up wandering through a dense forest near the foothills of Mount Fuji that attracts dozens of depressed people each year.

But before he can take his own life at the spot of his choosing, he encounters Takumi, a mysterious injured Japanese man who has lost his way.

- 'Profound cultural insult' -

Through conversations about their lives (mainly Arthur's, in fact) and flashbacks, Van Sant shows Arthur's downward spiral back in Massachusetts with an alcoholic wife (Watts) and a stalling academic career.

Takumi leads Arthur on a rough hike that becomes a spiritual journey to examine where it all went wrong, complete with dialogue offering platitudes about science not offering all the answers to life's questions.

A plot twist that most viewers saw coming and a sentimental ending accompanied by swelling string music seemed to nix Van Sant's shot at claiming a second Palme d'Or after his 2003 triumph with "Elephant".

Critics savaged the latest by Van Sant, who has been nominated for two Oscars -- for "Milk" and "Good Will Hunting" -- and attracted a cult following with "Drugstore Cowboy" and "My Own Private Idaho".

US movie website Indiewire said not even McConaughey could sustain the "mushy, amateurish story, which digs itself a deeper hole as it moves along".

"The established talents of both director and star only serve to magnify the many wrong moves that this stunning misfire takes," its reviewer Eric Kohn said.

"The bulldozers are out and subtlety will be crushed until not a crumb remains," French weekly L'Express said, calling its disappointment in the film "immense".

US trade journal Variety said the "risibly long-winded drama" was "perhaps above all a profound cultural insult", with Watanabe having "little to do other than moan in agony, mutter cryptically, and generally try to act as though McConaughey’s every word isn't boring him (pardon the expression) to death."

The Cannes Film Festival runs until May 24.