Labour has an "absolute responsibility" to try to form a government, even with a slim majority, leader Jacinda Ardern says.

Photo: RNZ / Claire Eastham-Farrelly

Ms Ardern told RNZ's Morning Report she had spoken to New Zealand First leader Winston Peters - who she said was in "good spirits" - but both parties were still waiting on the special votes result, due on 7 October.

"I share the same view as Mr Peters that those special votes matter enormously."

Based on historical patterns, National is likely to lose one or two seats once special votes have been counted, and Labour and the Greens could pick up one each - narrowing the gap between left and right blocs from six seats to as few as two.

That would increase a Labour-Greens-New Zealand First coalition's majority from 61 seats to 62 or 63 - a "more comfortable position", Ms Ardern said.

"Most leaders would want some comfort that they majority they hold could sustain, for instance, the loss of MPs. It doesn't preclude [Labour and New Zealand First] having those conversations but the specials matter."

However, a slim 61-seat majority still allowed Labour to be "in the frame", she said.

The National-led government had often relied on just one or two votes from support parties to get legislation passed, including government budgets.

She rejected a suggestion that Labour should build on its rise in support and instead target the 2020 election.

"I have an absolute responsibility. We campaigned to be in government, we campaigned for change," she said.

"The idea I would simply preserve my or Labour's political position for expediency is wrong."

Asked about speculation that National might try to form a coalition with the Greens, she said that was not a conversation or decision for her.

"But [the Greens] have certainly relayed to me that their expectation and their focus is on changing the government."