A New Zealand fitness instructor who got lost in rugged bush while taking part in a race drank her own breast milk and covered herself in dirt to survive a cold night.

Susan O'Brien, 29, of Wellington, was brought out of the bushland in the Westpac Rescue Helicopter at 11.30am on Monday, 24 hours after she was due to finish the race.

Her first duty after being rescued was to breastfeed her hungry eight-month-old daughter Meisha.

Ms O'Brien disappeared while competing in the XTERRA Wellington Trail Running Series in the Rimutaka Forest Park, Wainuiomata, on Sunday morning.