Prime Minister Chris Hipkins has attempted to seize momentum for Labour in New Zealand's election campaign, ruling out a coalition with Winston Peters' New Zealand First party.

The Labour leader has also lashed the policies of right-wingers ACT as "radical craziness" and painted poll leaders National as full of MPs "who want to roll back women's rights".

On Sunday, Mr Hipkins made a pointed pitch to retain office when he made clear his coalition possibilities after the October 14 poll.

Coalition-building is common in New Zealand, where at least two parties have been in government since 1996.

Under Mr Hipkins, Labour would be opening to governing with the Greens and the Maori Party, but not National, ACT or NZ First.

Polls show the contest is tight, with Mr Peters' NZ First possibly holding the balance of power.

The 78-year-old is closing in on a return to parliament, campaigning on fringe issues such as a rollback of transgender rights.

Under Dame Jacinda Ardern, Labour governed with NZ First during its first term in office, but Mr Hipkins said Mr Peters' party was now incompatible with his.

"Labour's focus in this election won't be on imported culture wars, but fighting an economic war against inflation and inequality," he said.

"New Zealand First has become a party more interested in toilets than the issues that really matter.

Labour's decision to rule out NZ First was widely expected.

However, in the first signs of Mr Hipkins' promise to "fight back" after a poor poll last week, he used the announcement to put the opposition in a tough spot, while rallying the faithful.

Mr Hipkins planted Labour's flag in the ground for the politics of inclusivity.

"Whether you're Maori, Pasifika, pakeha, gay, straight, born here, migrated here, a man, a woman, trans, young, old or different in your own way, I am in it for you," he said.

"I believe that a change in government now would not be good for a large segment of New Zealand society.

"That includes our rainbow community, it includes our Maori and Pacific people. It includes those on low incomes.

"It includes those who are relying on investment in our public services, our health care, our housing, our education."

Labour's decision puts pressure on alternative prime minister, National leader Chris Luxon, to make clear whether he could work with NZ First.

Speaking later on Sunday, Mr Luxon repeated his position over recent weeks, that it is a "hypothetical" he won't buy into.

Mr Hipkins said a three-way government between National, ACT and NZ First would be a "coalition of cuts, chaos and confusion".

"They are the coalition of fear," he said.

The Labour leader said members of National's caucus "celebrated" the loss of access to abortion in the US, while others wanted to "roll back women's rights".

"Christopher Luxon is refusing to rule out any of ACT's policies ... all of their radical craziness will be on the table under a government led by him," he said.

Mr Luxon said Mr Hipkins' attack was "desperate".

"It's incredibly sad that Chris Hipkins has decided to go so personal and so negative but I understand it because he has no record to run on and he has no ideas that take the country forward," he said.

Mr Luxon ruled out any change to abortion laws, funding, or access under a National-led government.

Polling suggests a tight race, with most recent surveys pointing to a National-ACT government with a slender majority.