Melbourne, Sept 10 : Elisabeth Fritzl, who was kept prisoner by her father Josef Fritzl for 24 years, has spoken for the first time of her horrifying cellar ordeal.

The 42-year-old bore Josef seven kids while being imprisoned in an underground cellar in Austria.

Elisabeth, who was finally freed in April, has told a judge investigating the case that she was raped up to three times a week by her father and if she tried to stop him, the children suffered.

She also alleges Fritzl scared the children by bullying them and threatened to leave them all to die in the cellar.

"He was very brutal against me," News. com. au quoted Elisabeth, as telling Austrian judge Andrea Humer during an interview, according to extracts printed in Britain''s Sun newspaper.

"And when I did not agree to have sex, then the kids would suffer. We knew he would kick us or be bad to us," she added.

Elisabeth, her eldest daughter Kerstin, 19, and sons Stefan, 18, and Felix, 5, were imprisoned in a concrete bunker underneath Fritzl''s family home in Amstetten.

Elisabeth''s three other children by her father - Lisa, 16, Monika, 14 and Alexander, 12 - were chosen by Fritzl to live upstairs with him and his wife.

Another baby boy she gave birth to in the cellar died soon after being born.

The six survivors were only freed after Kerstin collapsed on April 19 and was rushed to hospital after Elisabeth pleaded with her father to let her daughter see a doctor.

In her interview with the judge, Elisabeth said her father threatened to leave them to rot in the cellar.

"He said he could close the door whenever he wanted and then we would soon see how we survived," she said.

Elisabeth also told of how she tried to keep life as normal as possible for her children when their father was not around.

"When he went away we led our own lives," she said.

"When he was here it was all silence. He was just all-powerful. It was his kind of communication to use rough words. He would be insulting against me and the children. When he was at the table and we were eating and someone was holding their knife wrongly, or did not want to eat, there would be verbal abuse.

"He wouldn''t let the kids develop their own personalities. He would not allow the kids to have their own will," she said.

Fritzl''s trial is expected to take place later this year and it is thought he will face up to 3,000 rape charges. (ANI)