A bill legalising assisted dying has inched closer to becoming law, despite plans by critics for a long and messy battle.
Act leader David Seymour scored a win late in Parliament on Wednesday as changes he proposed to his fiercely contested End of Life Choice Bill passed 74 votes to 44.
The amendment narrows the bill to only give access to voluntary euthanasia to those with six months left to live.
After passing 70 votes to 50 at its second reading in June, the assisted dying legislation this week reached the committee of the whole House - a stage before the final vote where last-minute changes are considered.
Seymour had to put up a series of proposals limiting the bill in a bid to secure the votes he needs and assure MPs on the fence it's safe.
The legislation originally let terminally-ill adults or those with "grievous and irremediable" conditions request assisted dying, with clearance from two doctors.
Taking out the "irremediable" clause aimed to quell fears about implications of the law for the disabled community and to secure the Green Party's vote.
Those against the bill looked set to drag the process out on Wednesday, by promising to put up a swathe of their own amendments for the debate.
National's Simon O'Connor at the start of the night told the House he and others would be conducting a "clause-by-clause, word-by-word" interrogation.
"We get this wrong and people innocently die. I, for one, believe the number zero is fantastic. One would be too many," he said.
With no restrictions on the number of speeches MPs can make during the committee stage, it was unclear how long the arguments could drag on for.
But a ruling by Parliament's Speaker last week meant that - despite protests from National's Gerry Brownlee - Labour, the Greens and NZ First were able to force a vote late in the evening on a first round of changes.
A series of other proposals by Seymour also went through 75 votes to 42.
And because the House can't pass amendments that contradict each other, a number of changes sought by opponents, such as National's Chris Penk, Melissa Lee and Maggie Barry were thrown out immediately.
A number of others were voted down in a series of drawn-out conscience votes.
Afterwards, Seymour said it was still early days.
The bill will now return to the House on August 21 for debates on another four parts of the legislation, before going to its third and final reading.
"What's important is that we made really good progress ... We've completed one of five," he said.
MPs are voting on the bill and changes individually - rather than along party lines - and hours before the debate began, a group of National members ardently opposed called a press conference to outline how they would be submitting at least 120 amendments.
Led by Barry, they proposed changes including increasing the age of eligibility for assisted dying from 18 to 25, tightening the rules for declaring someone competent, and adding more references to cultural concerns.
"For the thousands of people who came before the select committee their issues have not yet been debated by the whole of the House," Barry said.
The justice select committee that considered the bill received a record 39,000 submissions, largely opposed, but ultimately couldn't decide on major fixes to the law, with Barry, its deputy chair, calling it unworkable.
But the critics were adamant they weren't just throwing out proposals to stonewall, despite threatening "amendments on amendments".
A 1 News Colmar Brunton Poll this week found 72 per cent of those surveyed believed "a person who is terminally or incurably ill should be able to request the assistance of a doctor to end their life".
The biggest obstacle to Seymour's bill may now come from NZ First.
The party is demanding a public referendum be a requirement of the legislation.
They will vote "no" on the bill if the House shoots the plebiscite down.
Despite trying to rally support for a referendum in recent weeks, Seymour says it's not clear it has the numbers to pass.
Without NZ First's nine votes, he cannot afford to lose even a single net "yes" from the second reading.