Mrs O'Brien spent the night drinking breast milk and covering herself in dirt

Searchers located the mum via helicopter with a heat detector on Monday

A mother-of-two who spent a freezing night in a forest after becoming lost during a marathon revealed she survived by drinking her own breast milk and covering herself in dirt to stay warm.

Susan O' Brien, from Johnsonville in northern Wellington, New Zealand, took off in the XTERRA Wellington Trail Running Series at the Rimutaka Forest Park at about 9am on Sunday.

The 29-year-old was expected to complete the track about two and a half hours later but she never crossed the finish line.

The alarm was raised at 11.30am, sparking an intensive search for the personal trainer.

She was found on Monday morning, about two and a half kilometres off the running trail, after searchers scoured the park and managed to locate her via helicopter with heat detection equipment.

Susan O' Brien pictured with husband Daniel and their childre just hours before the race started on Sunday

Mrs O'Brien told reporters she took a wrong turn, admitting she was bad with directions.

'I'm not a very good orienteering woman,' Mrs O'Brien said, according to NZ Herald.

Her distressed parents Andrew and Maggie Khoo, husband Daniel O'Brien and their children were reunited with Mrs O'Brien, who spent exactly 24 hours under the wet and freezing weather.

'I definitely thought I was going to die,' she said.

When she couldn't find her way back to the trail, Mrs O'Brien decided to dig a hole in the forest while covering herself with dirt in an attempt to stay warm and nourished herself with her own breast milk.

Her brother, Jack Khou, who previously posted a public appeal on his Facebook account, has thanked the search and rescue team who worked tirelessly to find his sister.

'A great day to be a New Zealander in New Zealand', he posted.

Her brother, Jack Khou has thanked the search and rescue team who worked tirelessly to find his sister

The 29-year-old mother of two spent the freezing night covering herself with dirt and drinking breast milk

After 24 hours of an intensive search, the personal trainer has been found safe and well on Monday

The organisers of the race also took to the XTERRA Trail Run Facebook page to announce the good news that Mrs O'Brien has been found.

'She is in good shape and is being helicoptered back to base,' the post said.

'We are all very relieved, especially for her family and of course extremely grateful to all the searchers involved, NZ Police and many offers from the running and wider community to help with the search. Thanks so much.'

On Sunday night, Mr Khou posted a photograph of Mrs O'Brien along with her husband Daniel and their children as they posed happily before the race.

The revelation comes after other runners scoured the race track twice before more than 30 people from the Land Search and Rescue team arrived with three search dogs, NZ Stuff reports.

The team had camped at the park in Wainuiomata, Lower Hutt overnight as they combed through the forest until 1.30am on Monday.

She was last seen wearing a pink headband, grey jacket, black 'Under Armour' tights and red/pink shoes.