Vienna  - Austrian authorities on Monday were continuing their probe into the arrest of a 73-year-old man believed to have fathered seven children with his daughter who he kept imprisoned in a dungeon for 24 years.

After Sunday's arrest of Josef Fritzl, a retired electrical engineer, police are investigating the basement dungeon under his house in the town Amstetten, where his daughter Elisabeth, 42, and three of her six surviving children had been imprisoned.

Investigations were continuing with all due care, police officials were quoted as saying by the Austrian press agency.

According to first reports the dungeon rooms were small, with a maximum height of 1.7 metres and equipped with sleeping cots as well as cooking and washing facilities.

It also included a padded cell, a local official said.

Josef had provided the police with the codes for the dungeon's electronic locks on Sunday.

Elisabeth had been sexually abused by her father even before her imprisonment in 1984, she said in a statement released by police. During her captivity, she gave birth to seven children. One infant died shortly after his birth.

Three of the children, aged between 5 and 19, were imprisoned with her for all their lives. The other three lived with their "grandparents" and attended local schools.

Josef had told authorities that his daughter, who he reported missing after her "disappearance," had deposited the infants at his doorstep over the course of several years.

Authorities expect the results of DNA testing aiming at verifying those suspicions later on Monday. First results were corroborating Elisabeth's story.

She and five of her children are being looked after by doctors and therapists. One daughter, Kerstin, 19, who is believed to suffer from a rare disease, remains in intensive care at the local hospital. (dpa)