Four-year-old Chloe Crump's breathing problems are so bad, sometimes she struggles to simply walk to the neighbourhood park.

But the plucky pre-schooler defied the odds - and her own mother's expectations - by climbing to the top of Mauao on Saturday as part of a fundraising drive for charity.

Chloe suffered from asthma and bronchiectasis and required nebulisers to help clear mucus from her lungs twice a day, as well as chest physiotherapy twice a day.

Mum Rachel Crump said the thought of Chloe scaling Mauao was a "huge challenge" for her daughter.

"I'd be lying if I didn't say I wasn't extremely worried about her going up because I know what condition her lungs are in," she said.

"Some days she can't even walk down to the park.

"But thankfully it was a day where she was clinically good and it was a sunny day. The conditions were right, which helped."

Chloe's trek was part of a wider challenge aimed at highlighting how keeping active was good for respiratory conditions and kept lungs healthy. Chloe committed to 100 days of exercise, with Mauao being the toughest task yet. Her 100-day challenge was also helping to raise money for the Asthma and Respiratory Foundation which has helped the Crump family since Chloe was very young.

Ms Crump said the foundation had been invaluable in its help, which offered a raft of services including testing, advocacy, support, and health information.

"They can't do that without the help from general public. It's something quite close to our hearts."

Ms Crump said Chloe's carers from the Beachkidz preschool education programme put the Mauao challenge to the family, and walked with Chloe as part of a group of about 15 dressed in blue to the top. Ms Crump stayed below to ensure Chloe was not distracted for her climb.

When the group returned to the bottom and told Ms Crump Chloe made it all the way, she could not believe it.

"I was hugely surprised. I was so proud of her. The moment she ran into my arms when she reached the bottom was something I will never, never forget," Ms Crump said.

"I didn't think she would make it up there. She did it. She did really well. "

Ms Crump said Chloe was sore and tired yesterday but keen to climb Mauao again.

"She said afterwards 'Mum, I went all the way up there and it was really high'. She was quite pleased with the efforts. She seems pretty keen to do it again so once we're a bit more settled after this, we will," Ms Crump said.

"I couldn't be prouder."

Respiratory disease in New Zealand

• Affects one in six New Zealanders, or 700,000 people

• Is the third leading cause of death

• Costs $6 billion each year

• Responsible for one in ten of all hospital stays

• Although bronchiectasis is much less common than other respiratory conditions, hospitalisation rates increased by 36 per cent between 2000 and 2015 to 28.6 per 100,000, and deaths doubled from 42 per year in 2000/01 to 96 in 2013.

- Asthma and Respiratory Foundation NZ