US actress Gena Rowlands, whose six-decade career garnered Oscar nominations and other acclaim, died Wednesday at age 94.

No official cause of death was immediately given, but her son Nick Cassavetes said earlier this year she had been battling Alzheimer's disease for five years.

The Oscar-nominated performer brought her deep range of emotion and expression to a number of original and moving films that are considered classics of US independent cinema, most shot by her late husband, John Cassavetes.

For three decades starting in the 1960s, the couple formed an enchanting and explosive on-screen partnership that explored themes of passion and self-destruction against a backdrop of alcohol and infidelity.

In what many consider her finest role, Rowlands captured to devastating effect a descent into mental illness in 1974's "A Woman Under the Influence," bringing her the first of two Oscar nominations.

"Incapable of an unreal moment," said Woody Allen of the actress, whom he cast in his 1988 film "Another Woman."

"Whatever I say about Gena isn't enough because she's so incredible," said Winona Ryder, quoted in the LA Times in 1992 when the two co-starred in Jim Jarmusch's "Night on Earth."

"There's a nobility, strength and class to her work that nobody else holds a candle to, and she's so beautiful -- you just kind of marvel at the way she moves."

Making it true

From her earliest work there were shades of Marilyn Monroe in Rowlands -- the blonde hair in a wavy bob, the arresting on-screen beauty, and the undertone of sadness and vulnerability in her performances.

But she always challenged the idea of women as objects of desire in her performances and came of age as Monroe went through her own struggles, finally ending with her suicide in 1962.

"She can just play. Give her anything and she'll always be creative. She doesn't try to make it different –- she just is," said Cassavetes in a 2001 interview collection.

"Gena is very dedicated and pure. She doesn't care if it's cinematic, doesn't care where the camera is, doesn't care if she looks good -– doesn't care about anything except that you believe her."

A woman falling

Rowlands was born on June 19, 1930, in Cambria, Wisconsin, into a cultured middle-class family. Her father was a state senator and her mother was a painter and occasional actress.

She enrolled in New York's American Academy of Drama and in 1953 met Cassavetes, a fast-talking and exuberant Greek-American. A year later they were married.

It was their collaboration that generated her stand-out performances, the highlight arguably being "A Woman Under the Influence," which also brought an Oscar nomination for Cassavetes as director.

Rowlands was captivating as housewife Mabel, who descends into madness after years of quiet, complicated dominance by her hardworking and silent husband, played by Peter Falk.

In a rare moment of defiance, and one of Rowlands's most memorable scenes, Mabel fights back, rising at the table after a meal of spaghetti with friends and family, pleading to everyone to stand up for her -- just this one time.

The room is silent, and soon Mabel is institutionalized. When she emerges she is a shadow of her former, vivacious self.

The impact of the film and Rowlands's performance "has resonated throughout the American cinema ever since," said The New Yorker in 2013, citing Martin Scorsese and Spike Lee as two Hollywood figures under her influence.

Glorious 'Gloria'

One of her last films with Cassavetes was the more irreverent "Gloria," a 1980 gangster comedy about a woman on the run from the mob, in high heels, wielding a revolver and with a small child in tow.

Taking on the role with evident glee, in turns self-mocking and entirely convincing, Rowlands earned a second Oscar nomination and the film was awarded the top prize at the Venice Film Festival.

In 1989, Cassavetes died from liver failure after years of alcoholism. Rowlands continued to make films and also worked in television, winning four Emmys.

She and Cassavetes had three children, all of whom have gone on to have careers in film and television. Her son Nick directed her in "The Notebook" alongside Ryan Gosling and Rachel McAdams in 2004.

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In 2012, she married her second husband, retired businessman Robert Forrest, and in 2015 was awarded an honorary Academy Award, the same year she retired from acting.