Critics are queuing up to praise Natalie Portman in her latest movie "Black Swan," the opening picture at this year's Venice film festival, with one review saying the performance "elevates her ... to a major star."

The 29-year-old plays a New York ballerina whose obsession with technical perfection takes a heavy toll on mind and body.

Finally chosen for a lead role after years of toiling in the shadows, Portman's character Nina is derailed when a new member of her dance corps threatens to steal the part.

With scenes of violence, elements of supernatural, a sex scene with her fellow female lead and an emotional rollercoaster ride, Black Swan has been described as a step up for the actress best known for her turns in the Star Wars series.

"Every film festival benefits hugely from a strong opening film, and they don't come a lot stronger than Black Swan," wrote David Gritten in Britain's Daily Telegraph.

"Powerful, gripping and always intriguing, it also features a lead performance from Natalie Portman that elevates her from a substantial leading actress to major star likely to be lifting awards in the near future."

Others also uttered the "A"-word, as festivals in Venice and Toronto tend to mark the unofficial start of the long buildup to the Oscars. "The film looks bound to win its star, Natalie Portman, plaudits and award nominations for her searing performance as the ambitious but insecure Nina," said Geoffrey Macnab of the Independent.

Kunis also lauded

Even The Hollywood Reporter's Kirk Honeycutt, one of a minority of early reviewers to criticize the movie, had warm words for its leading actress.

"In her acting ... you sense she has bravely ventured out of her comfort zone to play a character slowly losing sight of herself. It's a bravura performance," Honeycutt said.

Co-star Mila Kunis also wins praise for playing "a perfect alternate to Portman, equally as lithe and dark but with a smirk of self-assurance in place of Portman's wide-eyed fearfulness."

For director Darren Aronofsky, the largely positive response to Black Swan will come as a relief.

Although he won the coveted Golden Lion for best picture in Venice two years ago for "The Wrestler," his previous movie in the canal city, "The Fountain," was panned in 2006.

Portman said the demands of her latest role, noticeably darker than previous outings, did not mean a change of direction away from more mainstream Hollywood fare.

"With everything I do, I always want to learn something new and part of that too, I think, is never being a snob," she told Reuters in an interview.

"I never want to try and just make arty intellectual films. I love those, of course, as experiences, but I also love big, more traditional entertainment kind of movies."

Black Swan hits U.S. cinemas in December.