UPDATED 11.16AM Labour MP Jacinda Ardern has put her hand up to stand for Labour in Mt Albert in the likely by-election prompted by incumbent David Shearer's departure.

LISTEN ABOVE: Jacinda Ardern spoke to Larry Williams

Ardern is almost certain to be selected by Labour for the seat which has been held by Labour since it was created in 1946 and was former Prime Minister Helen Clark's stronghold between 1981 and her departure in 2009.

Shearer's move to head the UN's Mission in South Sudan in January means a byelection is likely early in the new year unless Prime Minister Bill English calls an early midwinter election - something he has indicated is unlikely.

If Ardern becomes MP for Mt Albert it will allow Labour to bring a list MP in in advance of the 2014 election - Labour leader Andrew Little is keen to get Raymond Huo back to give Labour some Chinese representation. That will mean both Maryan Street and Moana Mackey will have to forfeit their places ahead of Huo on the party's list.

Until Shearer's resignation, Ardern had expected to stand against in the marginal Auckland Central for the third time after losing to National's Nikki Kaye in 2011 and 2014. Kaye has a 700 vote majority - the slimmest in New Zealand. Kaye is still on leave being treated for breast cancer but has confirmed she will stand again.

Asked if Ardern was effectively conceding defeat to Kaye in Auckland Central, Ardern said "everyone knows I lost twice - the results are pretty clear. But no, it's not a concession. I still genuinely believe Auckland Central can be won and I intend to work closely with whoever is the new candidate if I get selected [for Mt Albert]."

Ardern said the seat had a good pedigree, but she had not yet been in touch with Helen Clark.

"I would love to get her advice because it was her home and her seat for so long. There's no doubt the seat has a wonderful history. I guess that's a happy coincidence of that seat."

She had recently moved into the Mt Albert electorate, but said the decision to switch her candidacy to Mt Albert had been a genuine dilemma because she had worked in Auckland Central for eight years and built up a good team.

The Green Party polls strongly in Auckland Central and it was in a mix of electorates in which a deal was being considered to help ensure Labour won the seat back.

Boundary changes before the 2014 election meant part of the old Auckland Central were now in Mt Albert, including Grey Lynn, Arch Hill and Westmere.

Shearer won Mt Albert in a byelection in 2009 after Clark's resignation to head the UN Development Programme in New York.