What began as a family holiday has become a "bizarre" missing person's case.

It’s one of the most bizarre missing persons cases police have seen in decades. A Victorian family of five embark on a holiday, without phones, bank cards or any real destination, only to suddenly separate in rural NSW.

The children, all adults, returned home. The mother, Jacoba Tromp, was taken to hospital in Yass after being seen wandering around in a “dazed and confused state”.  Her husband, Mark Tromp, remains missing, and it seems that he doesn’t want to be found.

Speaking on The Today Show this morning, one of those children, 25-year-old Mitchell Tromp, said it’s been “tough times” since his parents vanished.

“It’s nothing I’ve ever been dealt with before, but I’ve had a lot of family support around me lately,” he said. “Hopefully some good comes out of this and my Dad will come home, safe and well.”

When questioned why his father, 51, is on the run, Mitchell responded: “He’s scared that people are after him. He’s not in a good state of mind.”

Police confirmed last night that the couple were paranoid and in fear of their lives.

Jacoba and Mark Tromp. Images: Victoria Police.

The Tromps left their berry farm in Silvan, east of Melbourne, on Tuesday for what Mitchell has described as a "technology-free break". They drove north across the state border, stopping at Bathurst and Jenolan Caves, on the western side of NSW's Blue Mountains.

Four of them left their phones at home, while Mitchell had tossed his out the car window.

But as their parents seemed to become increasingly paranoid and distressed (behaviour the family has described as out of character), the children chose to abandon the trip, which they did so separately.

"It slowly got worse as the days went by. They were just fearing for their lives, and then [we] decided to flee," Mitchell told media, according to The Sydney Morning Herald.

What happened after that, remains a mystery.

When police arrived to the Tromp family home, they were met with a chaotic scene. The doors were unlocked, bank cards were still there and documents were scattered throughout the house.

Police have desperately searched for Mark, but to no avail. Their only significant lead is a suspected sighting of him that occurred on Wednesday night at Wangaratta, well north of the Blue Mountains.

According to The Sydney Morning Herald, a young couple reported being closely tailed by a grey Peugeot station wagon in the suburb of Merriwa Park around 10pm on that evening, before a man leapt out of the driver's seat and disappeared into the darkness. He fled in such a hurry that keys remained in the ignition.

Police are confident that man was Mark.

Jacoba Tromp, 53, is believed to be in a mental health facility today, having spent most of Thursday being treated in a hospital in Yass, north of the ACT. It's believed she arrived in the area by public transport, which she caught alone from Wangaratta.

Police have spoken with her briefly, but are treading lightly out of concern for her mental health.

Mitchell told media this morning that his mother would occasionally suffer stress, but never to the level he witnessed in the lead up to the trip.

“It was a build-up of different, normal every day events, just pressure and it slowly got worse as the days went by,” he told reporters, according to Fairfax Media.

“The best way to describe it is like a movie. I’ve never seen anyone act like this or conduct themselves in this way.

At a media conference on Thursday afternoon, Sergeant Mark Knight described the situation as a “very unusual case” and the most bizarre he’d seen in 30 years policing, reports The Sydney Morning Herald.

"When I see them, I'll sit them down and ask: 'What the hell happened there?'"