Drone images of the farm showed a cluster of buildings with a large vegetable garden on one side. The small property appeared to be ringed by a fence and largely obscured by trees. Dutch media reported that the family was made up of five adult siblings and their father.
De Groot told reporters the siblings were aged from 18-25. He said their mother is believed to have died "a number of years ago." Local police said in a tweet that officers visited the farm after being alerted by somebody "concerned about the living conditions" of its residents.
Police said they arrested a 58-year-old man who rented the property, but it wasn't immediately clear why or what his relationship was to the family. Police said he wasn't the father. Police investigating the farm found "a number of improvised rooms where a family lived a withdrawn life," De Groot said in a statement.
Local bar owner Chris Westerbeek told broadcaster RTV Drenthe that he called police after a man "with a confused look in his eyes," with unkempt hair, a long beard and old clothes walked in to his bar and ordered five beers for himself.
"He said where he came from, that he'd run away and that he needed help urgently," Westerbeek said. De Groot said the police investigation is looking into "all possible scenarios," but didn't elaborate.
He said the family was now "in a safe place receiving appropriate care and attention."