News outlet Stuff reports support for the Yes and No campaigns in the "reeferendum" is split at 49.5 per cent each, with one per cent saying "don't know".

The No campaign, which aims to keep the status quo, has an edge when just registered voters are counted, leading 50.8 per cent to 48.4 per cent.

The vote is being held alongside a similar referendum on euthanasia at the national election on October 17.

Voting and being on the electoral roll is optional in New Zealand.

The new poll, of 1300 voters, shows the closeness of the debate.

Each survey conducted by pollsters aligned with major TV network polling has put the prohibitionist campaign ahead, while most online polls show the opposite.

The vote is being held at the behest of the Greens, which made the referendum a condition of their support for Jacinda Ardern's Labour-led government back in 2017.

Ms Ardern is sitting on the fence on the issue, refusing to be drawn on which way she will vote, and with a surprisingly blank history on the topic.

That's drawn the ire of campaigners, hoping the country's most popular politician might intervene to tip the ballot their way.

Labour has offered its MPs a conscience vote while opposition National MPs are all voting against it.

Australian Associated Press