A 13-year-old boy lost for three freezing nights with his father in Tasmania's rugged south-west wilderness said they were lucky to be alive.

John Ward, 41, and his son Stephen were trying to complete the Scott's Peak circuit when they became lost on Monday.

They were found just before 1:00pm on Thursday.

Rescued bushwalker John Ward is taken by stretcher to a waiting ambulance in Hobart, his son Stephen is near the helicopter. ( ABC News: Georgie Burgess )

Mr Ward has mild hypothermia, but his son is well and in good spirits.

Stephen Ward said he and his father kept close to each other.

"It was tough; really, really tough," he said.

"We came across a hiker, he said we were on the right track, the one we were on, but it wasn't, we were on a big, big track."

John Ward sheds a tear of relief aboard the rescue helicopter when it arrived in Hobart. ( ABC News )

Stephen said he thought they were about 20 kilometres away from the camp site.

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"We were on flat ground for a bit, then we found a river and made a hut down there," he said. "We had a few muesli bars and stuff like that."

The teen said he feared for their lives.

"I thought we were on the way out," he said.

Speaking from his stretcher, an emotional John Ward thanked emergency services.

"They did a really good job, they're real heroes," he said.

The pair spent Wednesday in a creek bed and decided on Thursday to move to higher ground.

They had water with them and told police they also ate food left behind by other bushwalkers.

The pair put something reflective out on the ground to attract the attention of search crews.

Search coordinator Sergeant Chris Williams said the fact they had built a shelter "probably saved their lives."

"They've been able to protect themselves somewhat from the elements, from the heavy rain we had, they still did become wet and damp in that shelter."

Police said although they were novice bushwalkers they did the right things.

'You all need a medal'

On Facebook, Mr Ward's sister Alison said the family's prayers had been answered.

"What a huge relief it was to see this. A big thank you to everyone who made it possible for my brother and nephew to return home," she wrote.

Sorry, this video has expired Police, SES find missing Tasmanian bushwalkers

"You all need a medal and will have nothing but gratitude and respect from all of my family.

"Thank you to everyone for the messages, kindness and prayers ... they were truly answered.

"My family will be forever grateful."

Mr Ward and Stephen had been missing since Monday, with the official alarm raised on Tuesday about 8:00pm.

They were on what police had described as a "father-son bonding weekend" in Tasmania's rugged south-west.

Mr Ward's car was found parked at the Huon Campground, with a campsite set up nearby.

The camp site of John and Stephen Ward. ( ABC News: Peta Carlyon )

Grave fears were held for the Hobart residents, who were described as "inexperienced" bushwalkers and under-equipped, with temperatures in the region plunging to almost 0 degrees Celsius overnight and rain and snow on areas nearby.

Police said the pair had not done any bushwalking in Tasmania before, but had made an entry in a log book which indicated they were going to do the Western Arthurs Traverse which is a four to five-day walk.

John's mother, Wendy Ward, said she had not yet spoken to them.

"[I am] very, very relieved. It has been a terrible of couple of nights, we are all so relieved," she said.

"We have all been so worried. I am just too relieved and too overwhelmed.

"Thank you to all the SES and the helicopter [crew] and the police and everybody that had been looking for them. Thank you very much from all of our family."