Labour leader Jacinda Ardern has attacked ACT leader David Seymour's "ludicrous" suggestion New Zealand First leader Winston Peters could end up Prime Minister.

Mr Seymour told The AM Show host Duncan Garner it was "logically clear" Mr Peters has a path to power.

"Everything I've said on this matter adds up and makes sense," Mr Seymour told Garner.

"Being Prime Minister, becoming immortalised is the one big prize for Winston Peters that he hasn't previously had."

But Ms Ardern told Garner the role of Prime Minister was never up for discussion, and both Labour and NZ First were focused on policy discussions.

"I've repeatedly ruled out any assertion that the prime role of Prime Minister is on the table. It is not," she said.

"You know, I have noticed in the commentary there's a lot of discussion about roles, where actually our discussions have been heavily focussed on policy, on ideas, and what we want to achieve," she says.

"It does a bit of a disservice to assume that we're only focused on roles - the baubles of office."

Mr Seymour says "some of the people in behind [in Labour and National's caucuses]" have every incentive to accept Mr Peters as Prime Minister rather than sit in Opposition for another three years.

"It's not ultimately their [Bill English's and Jacinda Ardern's] decision. They need the confidence of their caucus and it's their caucuses that want to be in power," he says.

"Who's more desperate? It's hard to say."

However Ms Ardern said Mr Seymour was "stirring".

"To try and set up [a role] that both parties have removed as being part of the conversation somehow means that the other parties will have failed if they haven't negotiated it is ludicrous," she says.

"I think he's obviously on some kind of crusade to get a bit of airtime."

Newshub.