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

EARLIER: The adult children of a missing Victorian couple, last seen in NSW, are "shocked" and "confused" after a man was seen bolting from their car into parklands.

They reported their parents, Mark and Jacoba Tromp, 51 and 53, missing to Goulburn Police after the couple disappeared during a family holiday in the NSW central tablelands early 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.

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 scoured the park on Wednesday, but failed to find the man.

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, NSW police say.

Mr Jones said Mr Tromp, an excavator, and Ms Tromp, also known as Cody, ran a hobby farm.

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

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.