Jacinda Ardern: Five key moments as New Zealand PM

Here are five moments that marked the leadership of the 42-year-old Ardern, who declared Thursday: "I know that I no longer have enough in the tank."

- Baby makes UN history -

Ardern won accolades in September 2018 when she was photographed kissing and bouncing her then three-month-old daughter, Neve, inside the hall of the United Nations General Assembly -- the first such appearance by a baby in the organisation's history.

She was only the second prime minister to give birth while in office after Pakistan's Benazir Bhutto in 1990.

"I want to normalise it," Ardern told CNN.

"By being more open it might create a path for other women."

- Mosque attack -

Ardern won widespread praise for her response to the March 2019 Christchurch attacks, when a white supremacist gunman targeted two mosques during Friday prayers, killing 51 and seriously injuring another 40.

When she donned a headscarf and comforted victims' families after the shooting, it resonated globally. She would later describe it as a spontaneous gesture of respect to the Muslim community.

She also won plaudits for swiftly enacting gun law reforms and pushing social media giants to address online hate speech.

Ardern found herself again comforting a shocked nation nine months later when a volcanic eruption at White Island, also known as Whakaari, killed 21 people and left dozens more with horrific burns.

- 'Covid election' -

Ardern won a second term by a landslide in October 2020, snatching a clear parliamentary majority as she rode a wave of "Jacindamania" popularity underpinned by her handling of the Covid-19 pandemic.

Ardern, who cobbled together a coalition government in 2017, dubbed her second win "the Covid election".

She campaigned on her government's success in eliminating community transmission of the coronavirus, which at the time had claimed 25 lives in a population of five million.

New Zealand only fully reopened its borders in August last year. The total number of deaths attributed to Covid has now climbed to 2,437.

- Pandemic protests -

Two years after winning her second term, a small but vocal segment of New Zealand's population turned against Ardern's handling of the pandemic.

Across four weeks, starting in February last year, hundreds of demonstrators occupied the lawn in front of the distinctive Beehive parliament building in the capital Wellington.

Ardern refused to meet the protestors -- many of them espousing anti-vaccine conspiracy theories -- and said they were using "intimidation and harassment" to get their point across.

The demonstrations ended in a flurry of violence, with some people ripping up paving stones and hurling them at riot squad police who were attempting to clear the camp.

More than 100 people were eventually arrested, with Ardern later describing the situation as "incredibly difficult" and "challenging".

- Popularity wanes -

Ardern's popularity waned as she battled declining trust in government, a deteriorating economic situation, and a resurgent conservative opposition.

Recent polls put the centre-right coalition ahead, with elections to be held on October 14

The stress has been evident in recent months -- Ardern showed a rare lapse of poise when she was unwittingly caught on microphone calling an opposition politician an "arrogant prick".