Police say the 53-year-old was located in a Yass hospital on Thursday morning. Her husband, Mark, 51, remains missing.

Police believe Mr Tromp is in the Wangaratta area. 

The couple's children said earlier that they were "shocked" and "confused" after a man was reportedly seen bolting from their parents' car into parklands.

They reported their parents missing to Goulburn Police after the couple disappeared during a family holiday in the NSW central tablelands early on Tuesday morning.

Police have been told the Tromp parents and adult children all travelled from the couple's home in Silvan, in Melbourne's outer east, to the Bathurst and Jenolan Caves area early on Monday.

The parents and their children split up on Tuesday.

In a bizarre twist, a man driving the couple's grey Peugeot station wagon, with Victorian number plates WRG 756, was reported to have followed a young couple in Wangaratta about 10pm on Wednesday.

The young couple saw the man get out of the car and run into Merriwa Park.

Police, with the assistance of the Dog Squad, scoured the park on Wednesday, but failed to find the man. No one else was sighted with him.

Family friend Christopher Jones said the children, Ella, Mitch and Riana, all in their 20s, at first believed their parents may have been found with the car, but are now struggling to understand the "odd" development.

"They are shocked. They are very confused," he said.

"They aren't really sure what's going on."

The children hold "serious concerns" for their parent's welfare, police say.

NSW Police have handed the case over to their Victorian counterparts.

Mr Jones said Mr Tromp, an excavator, and Ms Tromp, also known as Coby, runs a berry farm.

Adding to the mystery , Victorian Police says the couple left personal possessions, such as bank cards and mobile phones, at home in Silvan.

Mark Chapman, from neighbouring Chappies Choice farm, said the pair's disappearance was "completely out of character".

He said the family had lived in the area for about 10 years and were very close.

"They're really friendly people. They're a pretty tight family, very honest I would say," he said.

"We've helped them out with a few things and they always help us out. They are that sort of people."

The website for Parkview Farm, Ms Tromp's redcurrant business, offers visitors the chance to come and pick their own berries.

"They all have their jobs on the property and they all work together," Mr Chapman said. "They've all taken a strong interest in the farm."

Mr Chapman said the family holiday may have been the last opportunity for a break before the berry season starts in spring.

"It's quite typical for farmers this time of year when you're not busy on the farm," he said.

A Victoria Police spokeswoman said the circumstances surrounding their disappearance remained unclear.

"Victoria Police continues to work closely with NSW police in the hope someone comes forward with information on their whereabouts," she said.

Mark Tromp is described as Caucasian, 185 centimetres tall, with a dark brown crew cut, clean shaven face and brown eyes.

Jacoba Tromp is described as Caucasian, about 168 centimetres tall, medium to heavy build, with a fair complexion and blonde shoulder-length hair.

Anyone who believes they have seen Mr or Ms Tromp should call triple zero.

Anyone with general information is urged to contact Crime Stoppers on 1800 333 000.