New Zealand Prime Minister Jacinda Ardern shocked the country on Thursday by announcing she would resign from office in a matter of weeks.

The 42-year-old – who steered the country through natural disasters, the Covid pandemic, and its worst-ever terror attack – said she no longer had "enough in the tank".

"I am human. We give as much as we can for as long as we can and then it's time. And for me, it's time," she said at a meeting of members of her Labour Party.

Ardern said she would step down no later than February 7, less than three years after winning a landslide election to secure her second term in office.

She added that the country will choose its next prime minister in a general election on October 14, and she would continue to serve as an electorate MP until then.

Since that 2020 peak of "Jacindamania", Ardern's government has struggled – its popularity hampered by soaring inflation, a looming recession and a resurgent conservative opposition.

"I believe that leading a country is the most privileged job anyone could ever have, but also one of the more challenging," Ardern said.

"You cannot and should not do it unless you have a full tank, plus a bit in reserve for those unexpected challenges."

Ardern won international acclaim for her empathetic handling of the 2019 Christchurch mosque massacre, in which 51 Muslim worshippers were killed and another 40 wounded.

Later that year she was praised for her decisive leadership during the fatal White Island (also known as Whakaari) volcano eruption.

Ardern was the second prime minister in the world to give birth while in office, after Pakistan's Benazir Bhutto in 1990.

She said she was looking forward to spending more time with her daughter Neve, who is due to start school later this year, and finally getting married to her partner, TV personality Clarke Gayford.

Australian Prime Minister Anthony Albanese led international tributes to Ardern, saying she had "shown the world how to lead with intellect and strength".

"She has demonstrated that empathy and insight are powerful leadership qualities," Albanese said.

"Jacinda has been a fierce advocate for New Zealand, an inspiration to so many and a great friend to me." (AFP)