Wellington woman Susan O'Brien is found safe and well after spending the night in the Rimutaka Forest Park after getting lost trail running.

Breast milk, thoughts of her family, and handfuls of dirt helped a lost Wellington runner survive a cold night lost in rugged Wellington bush.

Susan O'Brien, 29, of Johnsonville, had been missing for exactly 24 hours after she was due to end a race through the Rimutaka Forest Park.

The Westpac Rescue Helicopter had been hunting for about four hours and had just dropped in a land search party when they spied a figure waving frantically at the sky about 11.30am.

Cameron Burnell/Fairfax NZ Wellington woman Susan O'Brien is found safe and well after spending the night in the Rimutaka Forest Park after getting lost trail running. She was greeted by her family, husband Daniel O'Brien, mother Maggie Khoo, father Andrew Khoo and 8-month-old Meisha O'Brien.

"She was just standing on the edge of the bank waving at us," crewman Colin Larsen said. "She obviously looked very relieved, she looked quite cold and tired but certainly very relieved to be taken back to her family."

The rescue chopper landed in the shingly Orongorongo River bed 15 metres from O'Brien. Larsen said she was just south of the Haurangi Hut, where another walker had spotted her about lunchtime on Sunday.

She was flown straight back into her "extremely relieved" family's arms.

Cameron Burnell/Fairfax NZ Susan O'Brien is hugged by her mother Maggie Khoo on being found.

Her first duty after emerging safely was to feed her hungry 8-month-old daughter, Meisha.

O'Brien said she had drunk her own breast milk to keep herself nourished through a cold Sunday night. "I'm breast-feeding my baby so I had a bit of my milk, which I thought, that should help me keep going."

When she realised she was lost, she dug a hole in the dirt and covered herself with soil to keep herself warm.

xterrawellington.co.nz Susan O'Brien, with pink headband, before she headed out on the XTERRA Wellington trail run on Sunday.

"I just kept chucking dirt on top of me."

On being found, she was still wearing the minimal clothing she had started the race in.

She was reunited with her emotional family, including Meisha and 2-year-old son Jayden, at the search headquarters.

XTERRA course map in the Rimutaka Forest Park

O'Brien said she was not good at orienteering and thought she was "definitely" going to die.

"I thought of my baby and my son and my family."

It was a cold night and she didn't have a survival blanket to keep her warm. "For some reason I kept strong because I kept praying all the time."

The thought of her children also kept her going. "Nothing else mattered but my family. I felt God with me the whole time."

After the cold night, she found her way back to the Orongorongo track and was already on her way out when she spotted rescuers.

She considered making her own way out, but decided to take a ride in the helicopter. "I wanted to get to my family as soon as possible."

On emerging from the helicopter, she was met and hugged by her crying mother, Maggie Khoo.

The runner's family issued a statement on Monday afternoon, thanking the police, search and rescue teams and race organisers for "their tireless and unwavering efforts to find Susan".

"As a family we are extremely relieved and thankful that Susan has been found safe and well.

"Susan will be having some much-needed rest over the next couple of days."

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O'Brien was racing in Sunday's XTerra Wellington Trail Running Series in the Rimutaka Forest Park, Wainuiomata, but failed to return as expected at 11.30am.

Search teams began scouring the area about 1pm on Sunday, and returned at first light on Monday, with a helicopter equipped with heat-detecting technology.

Police said at 11am on Monday that a confirmed sighting of O'Brien, around lunchtime on Sunday at a hut considerably off the competition track, had been reported.

Early on Monday, O'Brien's friends and family waited anxiously for news of her safety.

Her brother, Jack Khoo, was at the staging area on Monday morning along with her husband, Daniel O'Brien. The family had barely slept overnight and had returned to the scene to offer any help they could, Khoo said.

Susan, a personal fitness trainer and an instructor at the Keith Spry pool and CityFitness gym group, was fit and healthy, he said.

Race organiser Mike Thomason said 423 runners went on the run on Sunday around 9am. O'Brien was expected to finish by 11.30am, but by midday it was discovered she had not returned.

Runners scoured the entire track twice after it was established she was not in the race finish area or back home.

Police turned up to start searching about 5pm.

The 20km race started with a technical 5km stretch, followed by 5km on a forestry road, 5km along a ridge line then 5km on a well-signed track.

The race organisers had robust procedures to check for missing runners and these kicked in as soon as it was noticed O'Brien was missing, Thomason said.

Nick Engleback, from Land Search and Rescue, said race organisers did a "really good job" of searching till the official search parties arrived.

A team of 31 people plus three search dogs were out on Sunday with a similar number searching on Monday. Fires were lit on Sunday night to act as beacons.

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