A 73-year-old Austrian man has confessed to imprisoning his daughter in a cellar for 24 years and fathering her seven children, police have said.
Police said Josef Fritzl also admitted burning the body of a baby that died at the house in Amstetten, Lower Austria.
Mr Fritzl has been taken to court while authorities are caring for the woman, now 42, and her six surviving children.
Photos of the man's basement show a concealed network of tiny windowless chambers which were soundproofed.
Prosecutors say Mr Fritzl is expected to be taken into protective custody after appearing before a magistrate.
The woman, Elisabeth, disappeared aged 18 on 28 August 1984 when, according to her testimony to police, her father lured her into the cellar, drugging and handcuffing her before locking her up.
She is reported to have been made to write a letter which made it look as if she had run away.
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The head of the criminal affairs bureau in Lower Austria, Franz Polzer, said Mr Fritzl had admitted sexually abusing his daughter repeatedly during the time he imprisoned her.
Mr Polzer said Mr Fritzl told investigators Elisabeth had given birth to seven children, including twins in 1996, but one died shortly after being born and that he had thrown the body into an incinerator in the building.
The surviving children are now aged between five and 19 years.
The cellar rooms, covering an area of approximately 60 sq m (650 sq ft), were equipped for sleeping and cooking, and with sanitary facilities.
A reinforced concrete door was built into the wall that separated the "dungeon" from the house and electronically locked - the code known only to the suspect, who provided his captives with food and necessities, police said.
KEY FACTS IN CASE
Elisabeth reappeared at home after disappearing 24 years ago
Six children she says are hers have been found and placed in care
One of the children, aged 19, is seriously ill in hospital
Elisabeth's father Josef Fritzl, 73, has been arrested on suspicion of incest and abduction
Police say Mr Fritzl confesses to imprisoning Elisabeth and fathering her seven children
Three of the children were kept in the cellar with their mother and had never seen daylight, police told a news conference.
The other three children were adopted or fostered by the suspect, after he forced Elisabeth to write a letter saying she could not look after the baby, according to police.
His wife, Rosemarie, with whom he had seven of their own children, appears to have been unaware of the alleged crimes.
The security chief for Lower Austria, Franz Prucher, said he had been down into the cellar where it was easy to understand how the abuse was not discovered.
"The cellar is very deep," he said. "There you can cry and nobody will hear, nobody. There you can cry as loud as you can, you can hear nothing."
The alleged abuse and Mr Fritzl's apparent double life came to light when the eldest of the children in the cellar, 19-year-old Kerstin, became seriously ill earlier this month and had to be taken to hospital.
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Aerial shots of the investigation scene
A television appeal by medical staff for the patient's mother was seen by Elisabeth on a TV set in the cellar and she urged her father to let her go to hospital.
Police arrested Mr Fritzl shortly afterwards and took all the children into care.
"If you look at him today, you would hardly believe he was capable of doing these things. This man led a double life for 24 years," said Mr Polzer.
He said it was incredible that it had been kept secret for all that time.
Both the father and Elisabeth say no one else had access to the cellar, according to police, who are appealing to anyone with information about Mr Fritzl to contact them.
Asked why the captives had not tried to escape before, Mr Polzer said one had to consider the fact that the woman was small and weak and even the eldest boy, now 18, was "a small boy, a weak boy".
"You have to put yourself into the situation of these people," he said. "They led a completely different life to ours, they do not know what we know. These children were born into the jail, they knew nothing else."
Kerstin is said to be in a coma in hospital.
The head of the intensive care unit at the Amstetten hospital, Albert Reiter, said the impact of her experiences would eventually become clearer.
"The connection between the effects of 20 years without daylight, the incest and other illnesses, we will research in the coming hours and days," he said.
The media were told the other children who had been kept in the cellar were in surprising physical health, but very pale.
The region's district governor, Hans-Heinz Lenze, said he had spoken to the five-year-old boy.
"He even told me how happy he was and how fantastic it was to ride in a real car," he said.
Journalist Andreas Wetz, of the daily newspaper Die Presse, told the BBC the suspect's neighbours in Amstetten, a small town about 130km (80 miles) west of Vienna, were in shock at the revelations.
"The man who is said to have done this, they said he was funny, he talked to neighbours, he might be a little introverted, but they had no idea that this person could do this," he said.
The BBC's Bethany Bell says the case is reminiscent of that of Natascha Kampusch, the Austrian teenager held captive in a cellar in a house in a Vienna suburb for eight years, who ran to freedom in 2006.
While police are not connecting the two cases, many Austrians are asking how such matters went undiscovered, she says.
Miss Kampusch, now 20, has offered to help the victims. She told Austria's ORF radio: "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."
Police said Josef Fritzl also admitted burning the body of a baby that died at the house in Amstetten, Lower Austria.
Mr Fritzl has been taken to court while authorities are caring for the woman, now 42, and her six surviving children.
Photos of the man's basement show a concealed network of tiny windowless chambers which were soundproofed.
Prosecutors say Mr Fritzl is expected to be taken into protective custody after appearing before a magistrate.
The woman, Elisabeth, disappeared aged 18 on 28 August 1984 when, according to her testimony to police, her father lured her into the cellar, drugging and handcuffing her before locking her up.
She is reported to have been made to write a letter which made it look as if she had run away.
Please turn on JavaScript. Media requires JavaScript to play.
The head of the criminal affairs bureau in Lower Austria, Franz Polzer, said Mr Fritzl had admitted sexually abusing his daughter repeatedly during the time he imprisoned her.
Mr Polzer said Mr Fritzl told investigators Elisabeth had given birth to seven children, including twins in 1996, but one died shortly after being born and that he had thrown the body into an incinerator in the building.
The surviving children are now aged between five and 19 years.
The cellar rooms, covering an area of approximately 60 sq m (650 sq ft), were equipped for sleeping and cooking, and with sanitary facilities.
A reinforced concrete door was built into the wall that separated the "dungeon" from the house and electronically locked - the code known only to the suspect, who provided his captives with food and necessities, police said.
KEY FACTS IN CASE
Elisabeth reappeared at home after disappearing 24 years ago
Six children she says are hers have been found and placed in care
One of the children, aged 19, is seriously ill in hospital
Elisabeth's father Josef Fritzl, 73, has been arrested on suspicion of incest and abduction
Police say Mr Fritzl confesses to imprisoning Elisabeth and fathering her seven children
Three of the children were kept in the cellar with their mother and had never seen daylight, police told a news conference.
The other three children were adopted or fostered by the suspect, after he forced Elisabeth to write a letter saying she could not look after the baby, according to police.
His wife, Rosemarie, with whom he had seven of their own children, appears to have been unaware of the alleged crimes.
The security chief for Lower Austria, Franz Prucher, said he had been down into the cellar where it was easy to understand how the abuse was not discovered.
"The cellar is very deep," he said. "There you can cry and nobody will hear, nobody. There you can cry as loud as you can, you can hear nothing."
The alleged abuse and Mr Fritzl's apparent double life came to light when the eldest of the children in the cellar, 19-year-old Kerstin, became seriously ill earlier this month and had to be taken to hospital.
Please turn on JavaScript. Media requires JavaScript to play.
Aerial shots of the investigation scene
A television appeal by medical staff for the patient's mother was seen by Elisabeth on a TV set in the cellar and she urged her father to let her go to hospital.
Police arrested Mr Fritzl shortly afterwards and took all the children into care.
"If you look at him today, you would hardly believe he was capable of doing these things. This man led a double life for 24 years," said Mr Polzer.
He said it was incredible that it had been kept secret for all that time.
Both the father and Elisabeth say no one else had access to the cellar, according to police, who are appealing to anyone with information about Mr Fritzl to contact them.
Asked why the captives had not tried to escape before, Mr Polzer said one had to consider the fact that the woman was small and weak and even the eldest boy, now 18, was "a small boy, a weak boy".
"You have to put yourself into the situation of these people," he said. "They led a completely different life to ours, they do not know what we know. These children were born into the jail, they knew nothing else."
Kerstin is said to be in a coma in hospital.
The head of the intensive care unit at the Amstetten hospital, Albert Reiter, said the impact of her experiences would eventually become clearer.
"The connection between the effects of 20 years without daylight, the incest and other illnesses, we will research in the coming hours and days," he said.
The media were told the other children who had been kept in the cellar were in surprising physical health, but very pale.
The region's district governor, Hans-Heinz Lenze, said he had spoken to the five-year-old boy.
"He even told me how happy he was and how fantastic it was to ride in a real car," he said.
Journalist Andreas Wetz, of the daily newspaper Die Presse, told the BBC the suspect's neighbours in Amstetten, a small town about 130km (80 miles) west of Vienna, were in shock at the revelations.
"The man who is said to have done this, they said he was funny, he talked to neighbours, he might be a little introverted, but they had no idea that this person could do this," he said.
The BBC's Bethany Bell says the case is reminiscent of that of Natascha Kampusch, the Austrian teenager held captive in a cellar in a house in a Vienna suburb for eight years, who ran to freedom in 2006.
While police are not connecting the two cases, many Austrians are asking how such matters went undiscovered, she says.
Miss Kampusch, now 20, has offered to help the victims. She told Austria's ORF radio: "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."
