A Labour leadership ticket of Jacinda Ardern and hard-nosed Maori MP Kelvin Davis is emerging as the most likely option if Andrew Little falls on his sword.

Little heads into a do-or-die caucus meeting on Tuesday morning after a shock admission that he offered to resign as leader over a string of disastrous polls.

Labour is staring down the barrel at an election rout and Little may not even make it back into Parliament if the party's vote slips further.

ROBERT KITCHIN/STUFF Labour leader Andrew Little is in big trouble based on the latest polls.

Little said on Monday his resignation was rejected by his senior MPs and he was committed to fighting through to the election. But his admission has caused a furore and may have damaged his leadership further.

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Stuff has been told caucus members are weighing up options should Little now decide his position is hopeless - and Ardern and Davis are the frontrunners.

HANNAH PETERS/GETTY IMAGES Labour's Kelvin Davis could be on the election ticket.

Ardern already outranks Little in popularity in some polls while Davis has been highly effective in the Corrections portfolio and has a hard-hitting public profile.

While rumours were swirling late Monday about the caucus doing the numbers, it is unlikely there will be a direct challenge unless Little agrees to go - and that is still an open question.

But an Ardern-Davis ticket is seen as unifying the caucus as well as boosting the Maori caucus influence to reward the Maori vote.

Labour has been hit by a series of hammer blows with polls showing its popularity taking a dive - even from its own pollster.

A UMR Research poll provided to Labour, the pollster's corporate clients and some other parties last week, and leaked to Stuff on Monday, showed Labour on 23 per cent - down six points from a similar poll in June.

That was worse even than Sunday's One News-Colmar Brunton's poll, which put the struggling party on 24 per cent and prompted leader Andrew Little to offer to quit, although his senior colleagues turned the offer down.

But there was no better news for Labour in a Newshub-Reid Research poll on Monday that also had Labour diving to 24 per cent.

The party's MPs will meet in Wellington on Tuesday to discuss the polls.

Much of the campaign policy has been set in place, and preparations for the September 23 election are well under way.

And Labour's MPs are publicly backing LIttle, despite the poor polls, and his Ardern was publicly staying loyal to him.

But within three months of the election Labour's caucus of MPs has the option of changing leaders quickly and cleanly without going through the drawn out "primary" system that gives unions and rank and file members a say.

Meanwhile the UMR poll had better news for NZ First which hit 16 per cent against just 11 in the Colmar-Brunton poll. NZ First was on 13 per cent in the Newshub survey.

But all three polls have confirmed the strong showing by the Greens since it released its welfare policy and co-leader Metiria Turei revealed she had lied about how many flatmates she had when she was on a benefit in the 1990s.

The Greens were on 13 per cent in the Newshub poll and 15 per cent in the other two.

However, the rise of NZ First puts it in the box seat to determine who will govern, with both a Labour-Green grouping and National needing his backing.

A slow erosion of National's vote to 42 per cent in the UMR poll means Prime Minister Bill English could not cobble together a Government with the support of his minor party allies ACT, United Future and the Maori Party.

However, the One News poll put National on 47 per cent which would give it close to enough seats in the House with the help of its support players.

Among the smaller parties the fledgling Opportunities Party did the best, scoring 2 per cent in two polls.

Little maintains he still wants the job, despite admitting he contemplated falling on his sword in the wake of Sunday's disastrous poll result.

"It's the honourable thing, given that result. But I have no less conviction in my determination to fight hard in this election, because of what's at stake for so many New Zealanders right now," he said.

But he has admitted that, with the party polling so low it was not credible for him to form a Government and become prime minister, even though technically it could be done.