Patty Duke, who won an Oscar as a teenager for her role in The Miracle Worker and became an activist for mental health causes, has died at the age of 69.

The actress died in Coeur D'Alene, Idaho, on Tuesday morning from sepsis after suffering a ruptured intestine, according to her agent Mitchell Stubbs.

Duke won acclaim as the young deaf and blind Helen Keller in The Miracle Worker first on Broadway, then in the 1962 film for which she won the Academy Award.

The following year she starred in her own sitcom, The Patty Duke Show, in which she played identical cousins Cathy for three seasons.

Her son, the actor Sean Astin, said there had been an outpouring of grief from fans after her death.

He said: "We're so grateful to her for living a life that generates that amount of compassion and feeling in others."

The Lord of the Rings star said his mother had suffered after suffering the ruptured intestine, but described her as a "warrior" throughout her life.

He said: "You watch this 4ft 10, tiny imp of a lady who's more powerful than the greatest military leaders in history."

Born Anna Marie Duke in Queens, New York, in 1946, Duke had a difficult childhood with abusive parents.

By the age of eight, she was under the control of her talent managers who kept her busy on soap operas and advertising campaigns.

During this period, they supplied her with alcohol and prescription drugs which exacerbated her undiagnosed bipolar disorder.

In her 1988 memoir Call Me Anna, Duke wrote about her condition and the treatment she had received which helped stabilise her life.

The book became a 1990 TV film in which she starred and she became an activist for mental health causes.

Duke also served as president of the Screen Actors Guild from 1985 to 1988, and starred in several stage productions including a 2002 return to Broadway in a revival of Oklahoma!

(Sky News)