A Whangarei runner clocked up 115 kilometres - almost three marathons - during a 15-hour charity run around the Hatea Loop.

Kirsty Hamlin started out at 5.30pm on Friday and finished her 25th and final lap at 8.19am on Saturday.

She said her measurement of the loop was about 4.6km, which works out to a total of 115km.

"It was the furthest I've done in one go before."

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Ms Hamlin is a keen runner who "has a tendency to try and solve all the world's problems" while she runs.

Last year, a couple of people close to her struggled with mental illness and, looking for a way to help, she came up with the idea to run 15 hours in the dark on the longest night of the year.

"It's an analogy to going through some of these tough times and coming out the other side."

She said while the shortest day and subsequent longest night was on Wednesday, Friday was the most sensible time to hold the event.

The 47-year-old and her 16-year-old daughter Zoe Watson signed up to the Auckland Marathon Charity Heroes initiative earlier in the year and nominated the Mental Health Foundation and Youthline as their respective charities.

Ms Hamlin wants to make more people aware of the Mental Health Foundation and their services.

"Wherever you are, whoever you are, it [mental illness] touches a lot of people."

Ms Hamlin said 45 people took turns supporting her around the loop. Some rode bikes, others used their feet. At one point, there were 14 people in support, providing light and conversation.

She said the support crew were part of the bigger analogy.

"In those [dark] times we can actually get through this with the support, whether it be family or professionals."

She said the hardest part of the night was about 36km in, when she was feeling "pretty rough" and had to sit out one lap. Miss Watson, who was part of the support crew, ran the lap in her mum's place.

Ms Hamlin had some laps of walking, but otherwise maintained a constant jog.

She said she got "pretty cold and wet" after it started raining at around 3.30am and didn't stop until around 8am. She timed the finish to coincide with the finish of the weekly parkrun.

Ms Hamlin raised $984 from cash donations and donations to her and Miss Watson's donation pages. She is yet to hear how much was raised via text donation.

She is taking part in the Auckland Marathon later in the year to raise more funds. To donate to Kirsty go to https://aucklandmarathon2017.everydayhero.com/nz/kirsty