Mystery grows over bizarre family road trip

Australian police are trying to piece together the bizarre circumstances of a family road trip that went terribly wrong.

Fearing they were being followed, the Tromp family fled to New South Wales, leaving their phones and credit cards behind.

Now, the trip has ended with the father missing, and the mother and daughter in hospital.

Brother and sister Mitchell and Ella Tromp struggle to explain the road trip's circumstances.

"Just the general stress of general life got a bit too much," says Ella Tromp.

"The best way to describe it is like a movie. I've never seen anyone act like this," says Mitch Tromp.

The family of five runs a red currant farm in Victoria.

Mitchell and Ella say the family was under increasing pressure and decided to go away together.

By the time the family reached New South Wales on Tuesday, parents Jacoba and Mark Tromp were increasingly paranoid.

"They believe they're being followed for whatever reason and [surveilled] electronically and physically, for whatever reason," says Detective Senior Sergeant Kevin Coghlan of Wangaratta Police.

At some stage the family split up, fearing their lives, and decided to flee.

On Thursday their mother Jacoba was found wandering the streets - she's now undergoing a mental health assessment.

Daughter Riana is also in hospital suffering from stress, and police fear for the safety for their father, who's still missing.

"He's not dangerous, he's my mate, he's my father, I love him," says Mitch.

And they're desperate for him to come home.