Canterbury Charity Hospital says a new extension will help it offer a better quality of services to thousands of people.
The hospital began operating out of a single building in 2007, offering free elective day surgeries and medical clinics to people who did not qualify for or could not afford other health care.
Since then, it has grown to four connected buildings, with a new purpose built reception area, kitchen and flat opened this week by patron Sir Jerry Mateparae and Christchurch mayor Phil Mauger.
The charity trust's chair and founder, Phil Bagshaw, said the hospital had treated well over 20,000 people since it opened.
He said the unmet need for elective surgeries in Canterbury and around the country was huge - the hospital could not keep up.
"There has been big demand since the health reforms of the 1990s [when there was a shift to prioritise acute care] and it's growing... People have been under-investing in health for 30 years.
"Elective surgery is very, very important. If it's left unattended, the complication rates get up, the costs rise, young people can't work and elderly people lose their independence sooner," Bagshaw detailed.
"In fact, it's been shown from massive studies in Europe that investing in elective care actually saves money."
The charity hospital's aim was to plug gaps in the public health system, he said.
"What the hospital offers each year changes as we reactively fill in [where the most need is]. Our main areas at the moment would be women's health, dental and probably the biggest area is investigating patients with rectal bleeding who need colonoscopies."
Bagshaw said this was particularly the case for young people who could not get access to the services they needed.
He also used to be a surgeon at the hospital and believed its expansion would benefit both staff and patients.
"We now have the space to cope with our 285 volunteers and patients as well... The other advantage we've got from the space here is we can now move a lot of the administration out of clinical areas to open up more clinical rooms in the main hospital block."
The flat would also allow the option of an overnight stay where needed.
Louise Burgess has volunteered at the hospital as a scrub nurse for almost the entire time it's been open.
She first heard about it through work colleagues in the public health system.
"I began in the New Year of 2008 and have been here ever since... It's a lovely place to work.
"It's good for the soul. That's why I do it, because I know there are people out there that I can't donate money to, so I prefer to actually give a skill I can help with," she explained.
Sir Jerry Mateparae said he could not believe how many services it offered the community.
"It's important because it delivers services to vulnerable people who, for the most part, just wouldn't be able to access the sorts of treatment that they need [without it].
"And it's just a wonderful example of people in the community doing good for their community," he said.
When the times comes, it will be hard for him to step away, he added.