Amstetten, Austria: A 73-year-old Austrian electrical engineer has confessed to holding his daughter captive in a secret, windowless cellar for 24 years and fathering seven children by her, police said on Monday.

The case, centred on a nondescript two-storey building in the industrial town of Amstetten, was reminiscent of that of Austrian Natascha Kampusch who spent eight years locked up in a basement before escaping in 2006.

Elisabeth Fritzl, 42, had told police on Sunday that her father, Josef Fritzl, lured her into the basement of the plain, grey block where they lived with other families in 1984 and drugged and handcuffed her before imprisoning her.

Three of her children, aged 19, 18 and 5, had been locked up in the basement with her since birth and had never seen sunlight, police said, raising worries about their physical and mental state. The younger two were boys, the eldest a girl.

"[Fritzl] has now said that he locked up his daughter for 24 years and that he alone fathered her seven children and that he locked them up in the cellar," Franz Polzer, head of the criminal investigations unit in the province of Lower Austria told Reuters by telephone.

Burning the body

Fritzl had also admitted to burning the body of one of the children when it died shortly after birth, said Polzer. Austrian media reported he had burned the corpse in a boiler.

Three of the children - two girls and one boy - were brought up by Josef and his wife.

Investigators were combing through the network of cells where the victims had been held captive. During the morning forensic experts in white uniforms and gloves carried out boxes of evidence from the house which is on a busy street with shops.

Fritzl had hidden the entrance to the cell behind shelves and only he knew the secret code for the reinforced concrete door, said officials.

Some parts of the dungeon were no more than 1.70 metres (5 ft 6 in) high and officials in Amstetten said the basement labyrinth contained a padded cell.

Photographs showed a narrow passageway leading into other rooms which included a cooking area, sleeping area and a small bathroom with a shower. A tube provided ventilation.

Amstetten, located in rolling hills about 130km west of Vienna, is an industrial town of about 22,000 people.

The case unfolded when the 19-year-old girl became seriously ill and was taken to hospital, prompting doctors to appeal for the girl's mother to come forward to provide more details about her medical history.

Fritzl then brought Elisabeth and her remaining two children out of the basement, telling his wife - who thought their "missing" daughter had chosen to return home, police said.

Elisabeth agreed to make a "comprehensive statement" to the police after receiving assurances she would have no further contact with her father, who she said abused her from the age of 11.

Kampusch, who spent her teenage years held captive, offered to help the victims and told ORF radio she might talk to the family.

"I can imagine that it is very difficult both for the mother of the children as well as for the wife of the perpetrator to get through this," she said.

The case has raised questions about how authorities and neighbours failed to notice anything unusual in the "house of horrors", not least because officials said Fritzl had over the years build extensions to the secret dungeon.

Another puzzle is how Josef's wife Rosemarie could have been unaware of what was going on.