Children holding a banner at a demonstration of support for the Fritzl family. Photo / Reuters

Children holding a banner at a demonstration of support for the Fritzl family. Photo / Reuters

The 19-year-old daughter of Austrian rape and incest offender Josef Fritzl is being eased out of the artificially induced coma she was put into more than a month ago, doctors say.

Kerstin Fritzl was unconscious when she went to hospital on 19 April. She was suffering from multiple organ failure due to a lack of oxygen. She was also having severe convulsions believed to be linked to her parents' incest.

Doctors said at the time that she was at risk of dying and put her into an artificial coma to help her recover.

Yesterday doctors said her condition had improved enough to enable them to initiate a "wake up" phase to gradually ease her out of the coma.

Dr Albert Reiter, the chief anaesthetist at Amstetten regional clinic where members of the Fritzl family are being treated said that, although Kerstin was still under intensive care, he had been able to reduce the dosage of the drugs which had kept her in an artificial sleep.

A hospital spokesman said: "The doctors are very optimistic about the future development but, at this stage, it is impossible to say how long it will take before she actually wakes up."

Kerstin is the oldest of seven children that the self-confessed rapist Josef Fritzl, 73, fathered during an incestuous relationship with his daughter, Elisabeth, that lasted more than 24 years. Fritzl has admitted kidnapping his daughter when she was aged 18 and holding her prisoner in a cellar beneath his home in Amstetten where he treated her as a sex slave.

Fritzl allowed three of their children, Lisa, 15, Monika, 14, and Alexander, 12, to live a "normal" life upstairs after he and his wife, Rosemarie, formally adopted them shortly after they were born.

One of their children, a boy called Michael, died shortly after birth and Fritzl incinerated the corpse in his central heating boiler. The three other children, Kerstin, Stefan, 18, and Felix, five, were forced to spend the whole of their lives in Fritzl's cellar until their release just over a month ago.

Doctors say Stefan and Felix are gradually adjusting to life in daylight and freedom and that they have started reading, playing computer games and table football. Last week, a teacher visited the brothers for the first time and started a series of rudimentary lessons.

After his release, doctors said Stefan was suffering from serious motor neurone problems and had difficulty moving. Kerstin was said to have suffered from severe screaming fits during the final stages of her captivity.