Hundreds expressed outrage on social media, including a number of MPs. But rather than withdraw the comments Mr O'Connor is doubling-down, telling Newshub on Monday he had nothing to apologise for.

"At one level saying youth suicide is bad, but saying other forms of suicide are acceptable, that's an inconsistency. That's always been the approach I've had," he said.

"You cannot allow suicide for some and prevent it for others".

Ms Ardern has in the past expressed support for ACT leader David Seymour's End of Life Choice Bill, which would give "people with a terminal illness or a grievous and irremediable medical condition the option of requesting assisted dying".

Mr Seymour himself called Mr O'Connor's comments "inaccurate and offensive", and Labour MP Grant Robertson called it "offensive, desperate and sad".

On Sunday afternoon Ms Ardern choked up while speaking outside Parliament at a rally marking World Suicide Prevention day.

Mr O'Connor said he didn't doubt Ms Ardern's sincerity, but said she should "also be sad about those who are old or depressed or disabled who are also looking to suicide", and called her views "inconsistent".

"The intention of taking one's life is called suicide. There are some who say that there are legitimate opportunities where it should be allowed, and we call that euthanasia or physician-assisted dying. So no, it's just an inconsistent approach."

Too late to say sorry

Mr O'Connor's opponent in the Tamaki electorate, Labour's Sam McDonald, says it's too late for Mr O'Connor to apologise now anyway.

"I think people make mistakes, and if he had apologised really quickly and deleted the Facebook status, I would have respected that."

Mr McDonald says he and Mr O'Connor get along "really well" when they meet on the campaign trail, and have always been "cordial and respectful" to one another.

"But seeing his post demonising Jacinda Ardern, who has a strong passion for youth suicide and helping young people, I thought was incredibly disrespectful. Even worse, it was disrespectful to the people who were protesting and who have lost loved ones to suicide."

Separate issues?

Hundreds gathered outside Parliament on Sunday to urge the Government to do more on mental health. New Zealand has one of the highest suicide rates in the world, with more than 600 victims in the past year.

Mr McDonald says suicide and euthanasia are only linked by the fact they both concern "life and death", but apart from that, they are totally different issues.

"To put them in the same basket is really simplistic. The way he's gone about that has gone beyond having a respectful argument about that, and he's turned it into a personal attack on someone - which is the very culture which adds to, I think, our high youth suicide rate."

Mr O'Connor answered many of his critics on Facebook, saying it's not his concern if some of them were offended.

"People can take offence to all sorts of things… it's for people who take offence to explain why. All sorts of things can be taken for offence, left right and centre."

He said much of the criticism has been "shrill".

He is yet to discuss the controversy with his party leader, Bill English.

Arden's response

Ms Ardern told Newstalk ZB on Monday morning euthanasia and suicide were "completely different issues".

"The 600 people in New Zealand who have taken their own lives will shock and appal all New Zealanders. The fact our mental health services aren't doing enough for those people, that's something we should be talking about this election.

"To draw then a comparison to the issue of the people having the ability to make choices about their own end of life if they're facing terminal illness, is absolutely a completely different issue again.

"I've said openly that I believe people should be able to make their own choices in those circumstances. Mr O'Connor disagrees, he chaired a select committee on this issue and disagreed there too. That's a conscience vote for us all."

Newshub.