New Zealanders have narrowly rejected a proposal to legalise recreational marijuana, according to official referendum results released today.

The "no" vote gained 50.7% support, compared to 48.4% in favour of legalisation, the New Zealand Electoral Commission said.

The figure for those opposed to recreational cannabis narrowed from the 53.1% recorded in preliminary data released last week, but still maintained a slim majority.

It also said final results from a second referendum to introduce euthanasia confirmed overwhelming support for the move, with 65.1% in favour and 33.7% against.

Prime Minister Jacinda Ardern, who voted in favour of both proposals, was sworn in for a second term today, as final election results showed her landslide victory was even bigger than previously thought.

The charismatic leader and her ministers made their oaths of office in English and Maori during a ceremony at Wellington's Government House.

"I would say simply that sitting at this table is Aotearoa New Zealand," Ms Ardern said, gesturing to her gathered team, in which women and Maori are strongly represented.

"They collectively represent a range of different perspectives, huge talent, enormous experience and, as you would expect in any time of crisis, a huge commitment to serving this country."

Ms Ardern has vowed to honour the results of the marijuana vote, meaning the issue is unlikely to be revisited in her current term of office.

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However, the closeness of the vote will encourage reform advocates, who argue that disadvantaged groups such as the Maori community are disproportionately targeted under current laws.

The dual referendums were held on 17 October, alongside the general election that returned Ms Ardern to power with a landslide majority.

New Zealand Prime Minister Jacinda Ardern with her Minister of Conservation, Kiri Allan and Governor-General Patsy Reddy during a swearing-in ceremony in Wellington today

She did not disclose her position on the recreational cannabis debate during the election campaign, although the 40-year-old did admit to smoking marijuana "a long time ago". 

Advocates of the bid to legalise cannabis expressed disappointment that the Kiwi premier did not reveal her support for the bill until after the vote.

The euthanasia law, which had bipartisan support, will come into effect in November next year.

New Zealand will join only five other countries that have legalised euthanasia - Belgium, Canada, Colombia, Luxembourg and the Netherlands.

It allows a mentally sound adult who has a terminal illness likely to kill them within six months and is experiencing "unbearable suffering" to request a fatal dose of medication.

The request needs to be signed off by the patient's physician and an independent doctor, with a psychiatrist called in if either has doubts about the person's ability to make an informed decision.