A recipient of one of the Australian Medical Association's top honours is among a group of doctors who have split with the organisation over WA's voluntary euthanasia legislation on the eve of the start of debate over the new law.

Key points: The Australian Medical Association opposes voluntary assisted dying

The Australian Medical Association opposes voluntary assisted dying But seven doctors have signed a letter of support for WA legislation

But seven doctors have signed a letter of support for WA legislation Opposition Leader Liza Harvey has yet to decide how she will vote

Emeritus professor Max Kamien has been a doctor for 58 years, was a professor of general practice at the University of Western Australia and counts the association's prestigious Hippocrates Award for excellence in medicine among his accolades.

He remains an Australian Medical Association (AMA) member, but disagrees with the organisation when it comes to voluntary assisted dying (VAD).

"I have been a doctor for 58 years and during that time I have had a number of people who have said to me 'when the time comes, you will know what to do' or 'I want help and I want it now'," he said.

"And I feel I have let those people down because I know what to do but I don't have the wherewithal to do it, and I don't wish to spend the next five years of my life in jail for trying to help a patient."

Professor Kamien was one of the signatories to a letter, by Doctors for Assisted Dying Choice, which was sent to WA MPs ahead of the start of debate on the law, which begins in State Parliament today.

"Recently I have been involved with two patients who had very severe neurological disorders," he said.

"One of them was a staunch Catholic who wanted to die. She could do nothing herself. She wanted to die, and she is a patient I felt I let down.

"The other patient was a person that I went to school with and he developed a very severe neurological disease.

"He could not talk, he could not communicate, he could not do anything. He did not want to die, and nobody wanted to kill him.

"The whole issue is that this is a voluntary event.

"Doctors for Assisted Dying Choice just want to help people that want to be helped. They do not want to impose upon them that they have to die."

Euthanasia bill 'the safest of its type', doctors say

The letter to MPs, signed by seven doctors including four AMA members, said the association's position was "inconsistent with the wishes of doctors as a whole".

"The AMA in WA has espoused the equally incongruous position of opposing VAD while, at the same time, claiming a role in its regulation," the letter stated.

"On careful analysis, we believe the bill before the House is excellent. It is undoubtedly the safest of its type ever put before a legislature."

The claim was refuted by AMA WA president Andrew Miller, who said "a minority" of doctors supported the legislation based on surveys it had conducted.

"We believe that the bill as it is should be rejected or significantly amended," he said.

"We need to carefully look at it and we need to tie it to palliative care funding. There are a lot of improvements to be made."

Harvey undecided after living through husband's cancer

As lobbying intensified ahead of the debate, Liberal Opposition Leader Liza Harvey was one of several MPs still yet to decide how she would vote.

Liza Harvey's husband died of cancer five years ago. ( ABC News: Benjamin Gubana )

She said the death of her late husband from pancreatic cancer five years ago had made the decision particularly difficult for her personally.

"He went from 80 kilograms to 52kg over a year, and I had pressure from relatives and friends saying 'why don't you do something about this? Why don't you finish this?'" she said.

"It is really a confronting debate."

Ms Harvey said she was disappointed the debate had become highly political.

"For me that has been particularly disconcerting because I know better than anybody what it is like to watch somebody die slowly of cancer," she said.

"And I have had people abusing staff and sending me abusive emails.

"It has been particularly confronting for me."