An Auckland doctor who has just months to live after being diagnosed with a terminal illness says it's time for euthanasia to be legalised.

Dr John Pollock said it was unfair that if he lived in Holland, Belgium or some American states he would have the option of ending his life if his condition deteriorated to a point where he was suffering, but in New Zealand he faces a death he cannot control.

He believes it is time for a law change so people facing death have the comfort of knowing they can control the end.

"The law as it stands in my view is cruel. It's outdated, it's cruel, it's unnecessary - it needs to be changed," said the former GP, who has metastatic melanoma.

"I think an individual has the right to choose for himself how his life goes and how it ends. I don't think that it is fair or it is moral for somebody else to suggest that they know better and that they have the right to determine that you may not be helped to die."

The 61-year-old, who retired from the Torbay clinic he was working at after being diagnosed in December, was told about four months ago that he might have six to nine months to live but said it was difficult to know what course his illness would take and when.

He said if he was "lucky enough to have a quick death" it could come in the form of a stroke or pneumonia.

"Unfortunately what can happen is you can get a really prolonged death."

Under the current law, some terminally ill patients were left in the "most appallingly wretched states, sometimes akin to those who died of starvation in Nazi concentration camps", Dr Pollock said. "Ironically if we allowed a cat or a dog or a horse to reach such a condition we would be breaking the law and risking a prison sentence."

When asked if he had ever helped a patient end their life he replied: "It's against the law." He said he did however know "a number" of doctors who had helped suffering patients.

"I don't see how a merciful doctor could not. The difference between relieving pain and euthanasia can be really quite small."

Dr Pollock, who is supported by his wife and two grown children, believes there are at least 600 New Zealanders who would take advantage of the right to end their lives each year if it was legal. He now wants to push for that to happen in the little time he has left.

"I really do believe strongly that that we ought to have euthanasia and I think it's time to push. I would feel that the last few months of my life were worthwhile if I could stimulate a push to change this cruel law.

"The law won't be changed in time for me and the only way that I can legally end my life before it is due to end is suicide and that's the cruelty of it - not only suicide but suicide alone because if I top myself with my family present then I put them at risk and I think that's hideous. It's very cruel."

He said the law would give terminal patients the comfort of knowing help was available - if they needed it.

"If it was legal now it would be a huge comfort to me. I'd have an arrangement with my doctor under certain circumstances she would euthanase me.

"I may not make use of it and that is a very important point to make ... just knowing it's there, just knowing it's a possibility is a huge comfort and relief."