Jacinda Ardern's no threat to me - Andrew Little

Andrew Little says promoting Jacinda Ardern to the deputy leadership won't be a case of keeping his enemies closer.

Ms Ardern is expected to take over from veteran MP Annette King, who announced the end of her 33-year career on Wednesday.

The 36-year-old won the Mt Albert by-election in a landslide, and an unscientific Newshub online poll suggested three-quarters of voters would be more likely to support Labour if she was in charge.

Mr Little said on Thursday he hadn't seen the poll, but doesn't consider Ms Ardern a threat to his position.

"I've never seen anybody as a threat," he told The AM Show.

"My whole role as leader has been to get the team functioning, working well. I think I'm pretty good at spotting good talent and getting them up, and I don't feel threatened by that.

"If I felt threatened by that, I wouldn't be a leader."

He's also not saying whether he'd stand down to let her take over should Labour fail to win September's general election.

"I'm not even thinking about that. I'm thinking about what's needed to get us victory on September 23. Things are going very well… I'm not thinking about succession right now."

Annette's decision alone?

On Monday, both Mr Little and Ms Ardern said there was no plan for Ms Ardern to replace Ms King as deputy.

On Thursday Mr Little dodged the question of whether he and Ms King had discussed her retirement before Ms Ardern's Mt Albert victory - only saying she came to him on Tuesday.

"Annette has been my deputy for two-and-a-bit years - we talk every day, we talk about a lot of things," said Mr Little.

"David Shearer's resignation at the end of last year was a bit of a surprise… Jacinda saw the opportunity to go into Mt Albert. That was the right thing to do, I backed her to do that. Then we had a weird kind of by-election campaign, but a great success for Jacinda."

Ms King, also appearing on The AM Show on Thursday, insisted it was her decision alone to retire.

"You know me - nobody's going to tell me what I'm going to do, I'll make my own decisions, which I did."