Jacinda Ardern says she's taken on the worst job in politics, but she's committed to bringing "relentless positivity" to the party and next month's election campaign.

An hour after being named leader after Andrew Little's resignation, Ms Ardern's message to Prime Minister Bill English is not to be complacent.

She's giving herself 72 hours to take stock of Tuesday's events before bowling head on into "vibrant" campaigning alongside her new deputy, influential Maori caucus MP Kelvin Davis.

They'll commit to core elements of the Labour campaign so far, but Ms Ardern has vowed to put their own stamp on it as well.

Within the party there's a renewed sense of optimism, including from Trevor Mallard who suggested Ms Ardern could take 10 points from National on current poll figures.

"You would have seen the press conference with the policy depth of (Helen) Clark and the wit of (David) Lange in a way that I haven't seen that level of competence in a potential prime minister for a long time," he said.

"I think she's fiercely intelligent, very much like Helen Clark in that way, but I think she's got the advantage of youth and vibe and an ability to connect, probably better than Helen did before Helen was PM."

Both Ms Ardern and Mr Davis were elected unanimously, following nominations by Mr Little and Grant Robertson respectively.

Despite his resignation from the leadership, Ms Ardern says Mr Little will remain a senior caucus member and minister in any government she leads.

Ms Ardern told reporters she had been genuine in her repeated statements in the past that she wasn't interested in the job, but things are different now.

"These are extraordinary circumstances," she said.

"Everyone knows that I have just accepted - with short notice - the worst job in politics. But I also welcome this job."

As to whether she's capable of leading a coalition of Labour, the Green Party and New Zealand First, Ms Ardern said she was the president of an international youth organisation with members from Lebanon, Palestine and Israel.

"I think I can do this," she said.

The Maori Party could also be a potential coalition partner after its president Tuku Morgan extended an olive branch, telling the new leaders they "need to work together or at least have a proper and meaningful discussion."

All eyes will now be on the next round of polls.

Two media polls this week put support for Labour at 24 per cent, while Labour's own pollsters, UMR, recorded 23 per cent.

Mr Little said as leader, he took responsibility for those numbers.

He wouldn't say whether he was personally disappointed by losing the possibility of ever becoming prime minister.

"In a leadership role and in politics ... you cannot plan a path," he said.

"You do your best, you put yourself forward and you make a contribution."

Mr Little indicated he hoped to remain in parliament but the party would need to consider his list position.

He's currently ranked number one with Ms Ardern as number two.

Mr Davis is not on the party list as part of a deal with other Maori caucus members for an all-or-nothing approach to the Maori seats, but that expected to change in line with Labour's constitution.