A 73-year-old Austrian who has confessed to locking his daughter in a windowless cellar for 24 years and fathering her seven children appeared before a judge yesterday.

TV satellite transmission dishes are set up close to Josef Fritzl's house in Amstetten in eastern Austria yesterday.

Investigators were searching the 60 square metre cellar beneath electrical engineer Josef Fritzl's two-storey home, Franz Prucher, head of security in Lower Austria said.

"Down there it is just chaos at the moment. We have to go over every detail very carefully," Prucher said.

Fritzl appeared before a judge in St Poelten, the provincial capital of Lower Austria, yesterday, who ordered that police could keep him in detention while inquiries continue.

Officials said Fritzl said nothing on the advice of his lawyer. He was calm when he arrived on Monday and had been put in a cell where he can be monitored in case he tries to commit suicide, said Guenther Moerwald, head of St Poelten prison.

Elisabeth Fritzl, 42, says her father lured her into the cellar of their home in 1984 and drugged and handcuffed her before imprisoning her.

Three of her children, aged 19, 18 and 5, had been locked in the cellar with her since birth and had never seen sunlight. The younger two were boys, the eldest a girl.

Three other children - two girls and one boy - were adopted and brought up by Fritzl and his wife Rosemarie.

Police said Fritzl had admitted to burning the body of a seventh child when the baby died soon after birth.

DNA tests have shown that Fritzl was the father of her six surviving children, police said yesterday.

"The result... shows that the six children, which the unfortunate Elisabeth Fritzl gave birth to in the basement, have all been undoubtedly fathered by her own father, the now 73-year-old Joseph Fritzl," Franz Polzer, head of the criminal investigation unit in Lower Austria, told a news conference.

"There are a million unanswered questions," Polzer, said. "How could he manage to live with what he had done? How did he fool everyone?" he said.

He said he did not blame authorities for missing the case. "I have not been made aware of any error on their part."

"Fritzl was a very cunning man. He not only fooled his wife, but officials, the police, everyone."

The case unfolded when the 19-year-old daughter became ill and was taken to hospital. Doctors appealed for her mother to come forward to give details of her medical history.

The doctor treating the young woman, Albert Reiter, said on Tuesday her condition was critical and her artificially induced coma would continue for several more days.

"Our patient is in a severely life-threatening condition which resulted from a lack of oxygen caused sometime between Wednesday and Friday when she was admitted," Reiter said.

"In addition to 20 years underground, 20 years with no sunlight, 20 years of psychological stress, come other factors like infection," he told German broadcaster N24.

Fritzl brought Elisabeth and her remaining two children out of the cellar after the young woman was hospitalized, telling his wife their "missing" daughter had chosen to return home.

Photographs of the cellar show a narrow passage leading to rooms that included a cooking area, with children's drawings on the walls, a sleeping area and a small bathroom with a shower.

Fritzl had hidden the entrance to the cell behind shelves and only he knew the code for the concrete door.

Authorities have been asking how events in the house, situated in a busy street with shops in the small industrial town of Amstetten, 130 km west of Vienna, passed unnoticed for so long.

(China Daily via agencies April 30, 2008)