There is no other way for either National or Labour-Greens to govern without getting Mr Peters' support - he would choose who gets power.

But he won't give any clues as to which way he'll swing - he said that's up to voters and he won't say anything more until Election Day.

"Doing stitch-up deals behind the public's back is what we've never done," he said.

"No one's got any idea what they're going to say next or do next and to tie yourself to a catastrophic campaign from some other party is stupidity."

The poll numbers show the political scenario is actually very close with just 0.9 percent separating National and Labour/Greens - that boils down to just a two seat difference.

In a 122 seat Parliament, 62 seats would be needed to get a majority.

It is almost all tied-up with National on 55 seats and Labour-Greens on 53.

Mr Key says the party's polling numbers are "broadly in line" with the past three general elections.

"We're dealing with substantial issues but we're making good progress - broadly I'm happy with that, but obviously we have to work hard to be the Government every day."

He didn't want to predict who would make up the next Parliament, but National's preference would be to work with the same parties it had in the past.

Labour leader Andrew Little says closing the gap has come down to people thinking the Government isn't in control of the housing crisis.

"People can't get a decent house, can't even rent a house and they're saying, this government's run out of answers. And they're looking to parties that do have a comprehensive plan such as we've put out," he said.

And Greens co-leader Metiria Turei pointed to the same issue - housing.

"New Zealanders are right. National is failing us when it comes to housing. They have no new ideas, they won't build more houses, they're not taking the crisis seriously.

"New Zealand families deserve better, they deserve a chance to buy their own home and having that stability of having rents they can afford," she said.

Mr Key says the poll shows the public knows the answer to the housing "issues" is supply - "build more houses".

"Over the next three years we'll be building broadly 85,000 homes - we've got the biggest building boom in New Zealand's history."

Mr Little also said people are seeing a change in the Labour Party itself.

"People are seeing that Labour's been reinvigorated, it's united, it's doing well, it's coming up with new ideas and I'm going to be continuing to campaign just on that basis," he said.