ACT's proposal to build a national cancer centre is being labelled a fantasy by an oncology professor.

The party is turning Paul Henry's idea of building a dedicated, centralised cancer facility, into policy, recently unveiling a plan to build a "Starship for Cancer" with campuses in Auckland and Christchurch.

ACT expected around $2 billion of capital investment would be required, with funding from public-private partnerships, donations, and existing Crown health investment.

It also planned to establish a philanthropic foundation to attract some of the funding, and get rid of a cap on donation tax credits.

But philanthropic funding was "magical thinking," according to University of Otago professor of cancer medicine, Chris Jackson, who said overseas models were typically funded by private patients.

He said while it was easy enough to raise money for a building, securing funding for an ongoing service was an entirely different challenge.

"Cancer care operational expenditure year by year, ongoing, is hundreds of millions of dollars, if not more.

"The idea of getting that amount of money from philanthropy year, on year, on year, is just magical thinking."

Jackson said there was a raft of ways to invest in cancer care, that in his opinion, should be prioritised over a large cancer hospital.

"First off the rank, would be a lung cancer screening programme which would meaningfully improve cure rates in lung cancer," he said.

"The next thing we could do is lower the ... screening age for bowel cancer. I don't see philanthropists lining up to fund that, either."

Jackson said New Zealand had a problem with access to cancer diagnoses, with one of the highest rates of late diagnosis among comparable countries.

He said early diagnosis was done in the regions and was adamant a central cancer facility would only exacerbate the current issues - by draining those areas of much-needed resources.

"This proposal is going to do nothing to help the person with bowel cancer in Invercargill, with breast cancer in Timaru, or prostate cancer in Gisborne.

"Those are the sorts of people who will miss out under this type of policy."

Jackson said New Zealand needed a structure that enabled people to receive cancer treatment close to home.

"Centralising care in one or two places for all cancers, is ... a crazy idea, really."