Northern Territory police say one of three people missing in central Australia for almost two weeks has been found alive after a tip-off led to the trio's car.

Key points: Tamra McBeath-Riley was found alive by a search team 1.5km from the bogged car the group had been driving

Tamra McBeath-Riley was found alive by a search team 1.5km from the bogged car the group had been driving Claire Hockridge and Phu Tran looked for help in a different direction and remain missing

Claire Hockridge and Phu Tran looked for help in a different direction and remain missing A note left in the car said the missing pair travelled westward, which has allowed police to narrow the search significantly

Tamra McBeath-Riley, 52, was found at a waterhole east of the Stuarts Well area, south of Alice Springs, late on Sunday afternoon, 12 days after she and two others — Alice Springs local Claire Hockridge and South Australian Phu Tran — set out on an afternoon drive.

Superintendent Pauline Vicary said a pastoralist had told police they had spotted tyre tracks nearby, and the air search for the missing group was redirected and spotted the vehicle and a note left inside.

The note was dated November 21 and mentioned they had been bogged and what direction they were going to travel in to find help, Superintendent Vicary said.

She said it appeared Ms McBeath-Riley had gone north of the vehicle and the others had gone west.

"She [Ms McBeath-Riley] has travelled about 1.5 kilometres from the vehicle and was in an area where there was some water, so sensibly she appears to have stayed where the water is and has been drinking that and that's probably what's kept her going until we've been able to locate her," Superintendent Vicary said.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 18 seconds 18 s Tamra McBeath-Riley was discovered near a waterhole south of Alice Springs

She said Ms McBeath-Riley was "in quite a good condition".

"She had located a waterhole and they had been drinking from that waterhole as well as boiling some of the water up to make sure they were hydrated," she said.

Ms McBeath-Riley was transported to the Alice Springs Hospital to receive treatment for dehydration and exposure.

"We are extremely relieved that we've located her alive," Superintendent Vicary said.

She said police had interviewed Ms McBeath-Riley to try and get more information about the missing duo.

Ms McBeath-Riley was found on Sunday afternoon. ( Supplied: NT Police )

Missing duo were heading towards Stuart Highway

Superintendent Vicary said the search area for the missing pair has been narrowed down significantly.

"Based on the information that we have at the moment, they're probably heading towards the Stuart Highway, which is about 22 kilometres from where the vehicle was," she said.

Alice Springs residents Claire Hockridge (right) and Tamra McBeath-Riley (left) were reported missing on November 23. ( Supplied: NT Police )

The search was ramped up at first light on Monday with two helicopters deployed to cover the new search area.

"It's quite a long way for them to walk [to the highway], they apparently did have some water with them when they left the car," Superintendent Vicary said.

"We're hoping they have found some other water sources across the way."

St John Ambulance regional manager Andrew Everingham said Ms McBeath-Riley's rescue was an "absolutely incredible story".

"It looks like she was suffering from dehydration, heat stroke, and some gastrointestinal complaints — but in relatively good spirits considering the ordeal she's been through," he said.

Mr Everingham said the rescue gave emergency responders hope of finding Ms Hockridge and Mr Tran alive.

"We've got a crew on standby in Stuarts Well today to assist with the search efforts and all of us are fingers crossed they will find these two people as well," he said.

Ms McBeath-Riley's blue Staffordshire terrier Raya was also rescued on Sunday afternoon.