A visiting Canadian doctor claims if New Zealand introduces euthanasia, it could result in children choosing to end their own lives without their parents' input.

Canadian palliative care physician Leonie Herx is in New Zealand to take part in a debate hosted by North Shore MP Maggie Barry on ACT MP David Seymour's End of Life Choice Bill, which would legalise euthanasia under strict circumstances.

Euthanasia has been legal in Canada since 2016, where it's known as medical aid in dying, or MAID. Since then about 8000 have chosen to end their lives this way, Dr Herx says, making up around 1.5 percent of all deaths.

She told The AM Show on Monday it took Belgium 16 years to reach that level, after legalising the practise in 2002.

"How did we get to this place in two years, so rapidly?"

Like Seymour's Bill, Canada has strict rules around who is eligible for euthanasia, including age, mental state, how much notice must be given, number of witnesses required, approval from medical professionals and their prognosis. There's a 10-day waiting period, applicants must be informed of other palliative options and consent can be withdrawn at any time - even as the fatal drugs are being readied for injection.

Dr Herx however says there are already moves to widen eligibility.

"We've had a Superior Court Justice who's said the reasonably foreseeable death clause does not apply - so prognosis is not to be a factor. So anyone with chronic disease, osteoarthritis for example, have been given permission to be euthanised. Now the Government has mandated a taskforce to look at extending the criteria to including mental health."

The Canadian law currently states that their natural death has to be "reasonably foreseeable", ruling out conditions like osteoarthritis and mental health.

It also states they have to be at least 18, but Dr Herx suspects that's about to change.

"The largest children's hospital in Canada - the Toronto Hospital for Sick Children - has already published their guidelines on how euthanasia will occur for mature minors. It includes if the child says they don't want the parent to know, the parent will be informed the child has died after they've received euthanasia."

Seymour was approached by Newshub to respond to Dr Herx's claims, but declined.  

Dr Herx also says there is discussion on whether to allow advance directives for euthanasia, eg. a person pre-approving their death if they're one day diagnosed with Alzheimer's or dementia and no longer considered sound of mind.

"These are the types of problems that I don't think anyone expected in Canada. It seems you could put a nice fence around it, but once you let the genie out of the bottle, unfortunately you can't put it back in."

Dr Herx, who has been working in palliative care for more than a decade, says Seymour's proposed law is "very similar" to Canada's.

"The reality on the ground is very different than this rosy picture that has been portrayed... Learn from Canada's mistakes."

Whether New Zealand legalises euthanasia will be decided by a conscience vote in Parliament, where MPs don't have to vote along party lines. The End of Life Choice Bill passed its first reading 76-44, but MPs will often vote for a Bill in the first round so it can go to select committee, and this isn't always an indication of how the final vote may go.

Ninety percent of submissions at the select committee stage opposed the Bill, though scientific polls have a majority of Kiwis in favour of some form of assisted dying.