Assen: A father facing charges of sexual abuse in a Dutch court had held six of his nine children captive for nearly a decade at an isolated farmhouse, telling them "bad spirits" would enter their bodies if they talked to outsiders, prosecutors allege.

Gerrit-Jan van Dorsten, 67, is charged with unlawful detention, child abuse and money laundering. Now ailing after a stroke, he cannot speak and did not attend the pre-trial hearing in the city of Assen during which his custody was extended by three months.

The Netherlands farm where a six-member family was found in October. Credit:AP

In October, police found Van Dorsten and five adult siblings at the farm in Ruinerwold in the northern Netherlands after a sixth sibling escaped and reached a nearby village bar. Local people alerted police.

"All the children report physical punishment if they were deemed to be under the influence of spirits. This happened from a very young age, with children as young as four or five years old," prosecutor Diana Roggen told the judges on Tuesday, local time.