UPDATE: Simon O'Connor has now responded to the criticism. Newshub's earlier story is below.
National MP Simon O'Connor has accused Labour leader Jacinda Ardern of being "happy to encourage the suicide of the elderly, disabled, and sick".
The MP for Tamaki made the comments in a post on his Facebook page late on Sunday night.
"It's strange that Jacinda is so concerned about youth suicide but is happy to encourage the suicide of the elderly, disabled, and sick," he wrote.
"Perhaps she just values one group more than the others? Just saying."
Ms Ardern has 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".
On Sunday afternoon she choked up while speaking outside Parliament at a rally marking World Suicide Prevention day.
She told Newstalk ZB on Monday morning they 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."
Mr O'Connor's post was widely condemned on social media and by politicians on both sides.
Mr Seymour said it was "inaccurate and offensive" to conflate the "totally different issues".
Labour MP Grant Robertson called it "offensive, desperate and sad".
"The fundys are infiltrating the party. There will need to be a purge," right-wing political commentator Matthew Hooton tweeted.
"Charming," Labour general secretary Andrew Kirton wrote sarcastically.
"Oh man, I actually like you @SimonOConnorMP - but your FB post trivialising youth suicide and misrepresenting euthanasia is disappointing," wrote Auckland Councillor Richard Hills.
Among his own followers on Facebook, the post has had more 'angry' reactions as 'likes'.
Mr O'Connor replied to several followers, defending his controversial post.
"I am not the one saying suicide is acceptable in some situations. It is never the solution to any problem," he told one person.
"Those who support euthanasia... are arguing that suicide is an acceptable solution to some problems. I disagree."
'A line was crossed' - opponent
His Labour rival for the Tamaki seat, Sam McDonald told Mr O'Connor his post was "rubbish", but Mr O'Connor didn't back down.
"She has been on record supporting the suicide of the sick, elderly, and disabled. Either she is opposed to suicide or she is not," the National MP wrote.
Mr McDonald later posted on his own Facebook page that a "line was crossed".
"I know I can do a much better job."
Mr O'Connor was on a health select committee which earlier this year recommended no changes to New Zealand's euthanasia laws.
Newshub has been unable to reach Mr O'Connor for comment.
Prime Minister Bill English says there is a difference between suicide and euthanasia but he respects that Simon O'Connor has strong views.
If you wish to talk to someone about mental illness or domestic violence, you can call Lifeline on 0800 543 354, the Depression Helpline on 0800 111 757 or the National Telehealth Service on 1737.