The Prime Minister will not yet commit to legalising marijuana, even if the public votes for it in a non-binding referendum.

Photo: AFP

The government is debating when to hold the referendum.

While it would be cheaper to hold the vote at the next General Election in 2020, some politicians did not want the marijuana debate to dominate the election campaign and said it should be held in 2019.

Prime Minister Jacinda Ardern said the referendum - which was part of Labour's confidence and supply agreement with the Green Party - was in the "early days" of drafting.

"We haven't even drafted the question yet so that's all part of the work that we need to do.

"But of course we're asking the question of the public because we want to know where New Zealanders' sentiments lie."

The deal with the Green Party only specified the referendum would be held, not that the law would be changed if the public voted in favour.

Photo: RNZ / Rebekah Parsons-King

Green Party co-leader James Shaw said the government should listen to the public if it voted to legalise marijuana.

"I mean, there's not a lot of point holding a referendum if you don't pay any attention to the result."

It was still in the "very early stages" of planning what the phraseology would be and what the model would be, he said.

New Zealand First leader Winston Peters said his party's view was the vote should be binding but would not indicate which way he would vote.

"Look, this is a serious answer. I wouldn't contaminate a referendum by saying which way I was going to vote.

"What I want to do is give people the democratic choice and not have it imposed like so many of these social issues by a group of temporarily empowered politicians."

Act Party leader David Seymour said the result of the referendum must be respected.

"I think if you're going to spend tens of millions of dollars on a referendum then we've got an obligation to follow what the people want."

National Party MP Mark Mitchell said while the timing of the vote was up to the government, to save money he was leaning towards holding it at the next election.

Mr Mitchell said he would vote against legalising marijuana, but wanted more detail around what was being proposed.