A sign of the times, NZ PM Ardern's resignation resonates for women in power

Holding back tears as she made her declaration, the 42-year-old politician said she had next to nothing left "in the tank" and it was time to step aside after a challenging 5-1/2 years in office.

"Politicians are human," she said. "We give all that we can, for as long as we can, and then it's time. And for me, it's time."

But the remarks that followed were more revealing, said Anne-Marie Brady, a professor of politics at New Zealand's University of Canterbury.

Directly addressing her family in her speech, Ardern said she was looking forward to being around when her young daughter Neve started school soon, and finally marrying her partner Clarke.

"She was just very upfront and relatable," added Brady. "I think any young woman that has grown up in this era where we can have it all, yes, but actually we still have our heart connections to our loved ones."

Women have been liberated but "patriarchal institutions" have not evolved enough to support family life, she said.

"We need people like Jacinda Ardern in politics. So, her situation is cause for reflection about what we can do more to support women in politics, and men and their family life too," Brady added.

During her time in office, Ardern has not been afraid to break the mould, becoming the first prime minister since Pakistan's Benazir Bhutto to have a baby in the job and then take maternity leave.

A politician who campaigned on making tertiary education partially free, tackling child poverty and decriminalising abortion, Ardern has also called out blatant sexism in politics.

After meeting Finnish Prime Minister Sanna Marin last November, she dismissed a suggestion by reporters that their similar age and gender was the reason for the meeting.

"She shifted the face of politics globally just by being her," said Marian Baird, a professor of gender and employment relations at the University of Sydney.

"I think she has been a bit of a model for younger female politicians and perhaps even younger male politicians who want to present in a different way," she said. "Certainly she really challenges the male stereotype of being a prime minister."

'ALWAYS LED WITH HER HEART'

Despite her high profile globally, Ardern's popularity had waned domestically, hurt by rising living costs, growing crime and concern about social issues. Read full story

In the wake of her resignation she has been lauded as a leader who bought grace and generosity of spirit to the job, particularly amid challenging political times.

Former Prime Minister Helen Clark said Ardern had done an "extraordinary job" in leading New Zealand through major crises.

She delivered on a key social and economic agenda, and positioned the nation as one that "stood for co-operation and decent values".

"The pressures on prime ministers are always great, but in this era of social media, clickbait, and 24/7 media cycles, Jacinda has faced a level of hatred and vitriol which in my experience is unprecedented in our country," Clark said in a statement.

"Our society could now usefully reflect on whether it wants to continue to tolerate the excessive polarisation which is making politics an increasingly unattractive calling."

Cambodian opposition figure Mu Sochua said the world had lost a leader who commanded trust and respect, and "always led with her heart".

Yenny Wahid, a prominent Indonesian activist for women's rights and director of the Wahid Institute said Ardern's decision carried an important message for the next generation of leaders.