Actress and singer Patty Duke, who won an Oscar at age 16 for her portrayal of deaf-blind political activist Helen Keller in The Miracle Worker, has died aged 69.

“This morning, our beloved wife, mother, grandmother, matriarch and the exquisite artist, humanitarian, and champion for mental health Anna Patty Duke Pearce closed her eyes, quieted her pain and ascended to a beautiful place,” her son, the actor and director Sean Astin, said in a statement.

“We celebrate the infinite love and compassion she shared through her work and throughout her life.

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“Her work endures.”

Mr Astin did not give the cause of death but her manager said she developed sepsis from a ruptured intestine, according to media reports.

Duke, who lived in New York, shot to fame with a best supporting actress Academy Award for her role as Keller in Arthur Penn’s 1962 biopic The Miracle Worker.

She built on her success by playing “identical cousins” in her own sitcom, The Patty Duke Show, which ran for more than 100 episodes in the mid-1960s.

She went on to take film roles including in Mark Robson’s 1967 drama Valley of the Dolls, embarked on a successful singing career and served as president of the Screen Actors Guild from 1985 to 1988.

She won three Emmy Awards, including for the miniseries Captains and Kings and television movie My Sweet Charlie, which both aired in the 1970s.

In her 1987 autobiography, she revealed that she had been diagnosed with bipolar disorder, then known as manic depression, five years earlier, and she went on to become a vocal advocate for people with mental health issues.

Duke, whose real name was Anna Pearce, apologised to fans earlier in March for having kept a low profile recently.

“I have been absent, but not far, believe me. I love and miss you all. Hopefully back more soon and often,” tweeted the star, who celebrated 30 years of marriage to her fourth husband, drill sergeant Mike Pearce, two weeks ago.

“My mother’s life touched tens of millions of people,” Astin, who starred as Samwise Gamgee in Peter Jackson’s Lord of the Rings trilogy, said.

“Her groundbreaking portrayal of iconic American legend Helen Keller launched a career that would span six decades.

“First on Broadway and then on the silver screen, Patty Duke’s characterisation of the extraordinary development of the blind-deaf child brought global attention to the plight of people living with those challenges.”

Astin said Duke had talked about setting up a “Patty Duke Mental Health Initiative” before her death.

Flowers are being readied to be placed on Duke’s Walk of Fame star on Hollywood Boulevard.

Very saddened on the passing of Patty Duke. She was a wonderful friend on Twitter. Condolences to her family.

— William Shatner (@WilliamShatner) March 29, 2016

Patty Duke has died. Thank you for sharing your talent with us for all these years. #neelyoharaforever pic.twitter.com/sCrArGVbT1

— rose mcgowan (@rosemcgowan) March 29, 2016