New Zealand Prime Minister Jacinda Ardern has spoken about her sense of "betrayal" to the electorate that she had formerly contested.

Ardern said this morning that shifting to win the Mt Albert seat - after the departure of former Labour leader David Shearer - felt like a betrayal after years trying to win Auckland Central.

The mitigating factor was that with boundary changes a chunk of Grey Lynn moved too, she told the audience at an Auckland Writers' Festival event this morning.

Ardern was speaking at the event about the weeks leading up to the 2017 election that saw her form a coalition deal with NZ First and the Greens to form government - against most expectations.

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She "felt like it was my fault" that Annette King decided not to contest the 2017 election.

Ardern said after Andrew Little suggested she replace him as leader she said no for four days.

He had said to her - just before she was due to enter the debating chamber at question time - "I don't know if I can do it", meaning turn public opinion in support of Labour before the 2017 election.

She said she pushed back against Little's wanting her to become leader but eventually he didn't give her a choice and made a captain's call.

Political scientist Stephen Levine's book Stardust & Substance is being discussed at the festival.

Asked by writer Toby Manhire what she was reading she said that - other than Cabinet papers - she was reading material in a psychology journal about the aftermath of the Christchurch massacre.

The ASB Theatre at the Aotea Centre where she is being interviewed by Manhire is near full.

Ardern said she had texted her congratulations to Scott Morrison over his win in the Australian election, but she hadn't had a chance to phone him yet.

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Jacinda Ardern said she received so much
Jacinda Ardern said she received so much "feedback" on her hairdo during the election debate with Bill English she never repeated the hairstyle. Photo / Getty Images

Ardern, recalling the 2017 election debates in New Zealand, said she had a lot of respect for former prime minister Bill English.

She said it had been a "good clean fight".

Ardern had "angsted" a lot about what to wear. She wore her hair up for the first debate and received so much "feedback" that she didn't repeat the hairstyle.

Manhire asked if Labour would avoid buying Facebook advertising at the next election if it didn't behave better. Ardern said Facebook might or more likely might not take notice of that. She indicated the Christchurch Call to Action might be more effective, noting the pressure sovereign wealth funds worth $5 trillion, including the NZ Superannuation Fund, were applying.

Asked about baby Neve's favourite books, mum Ardern said her daughter liked paper. Cabinet papers often looked dog-eared after some time at home.

Ardern received rapturous applause at the end.