Six young adults and their father are receiving medical treatment after Dutch police acting on a tip-off discovered them locked away in a secret room at an isolated farm.
The six, aged 18 to 25, and their ailing father were found near Ruinerwold, a village in the northern province of Drenthe, local Mayor Roger de Groot said.
Officials in the Netherlands said they had apparently had no contact with the outside world for nine years.
Mr De Groot said a 58-year-old man, not the father of the children, was arrested at the farm. His role was unclear.
"As far as I know their mother died before they arrived there," he said. "Police found makeshift living quarters where the family was living in hiding."
The family, who according to local news reports had been waiting for the end of time, was discovered after one of the siblings escaped and sought help at a nearby cafe.
An employee at the cafe told RTV Drenthe one of the family members, a 25-year-old man, had come in looking scruffy and bewildered with long hair and said he had not been outside for nine years.
"You could see he had no idea where he was or what he was doing," the cafe owner, Chris Westerbeek, told the broadcaster.
"He said he had run away and that he urgently needed help."
The siblings and their father, who was reportedly bedridden after a stroke, were receiving treatment at an undisclosed location, the mayor said.
"I understand there are a lot of questions," Mr De Groot said.
"We have many too. The police are investigating all possible scenarios."
The siblings had apparently lived in a hidden cellar and survived on vegetables and animals tended in a secluded garden, local media reported.