New Zealand's former COVID-19 response minister Chris Hipkins will replace Jacinda Ardern as prime minister after receiving the only nomination from fellow MPs, the ruling Labour Party said Saturday.

The 44-year-old senior politician must be formally backed by Labour members of parliament on Sunday to take over as the country's 41st prime minister, following Ardern's shock resignation on Thursday.

The police and education minister will lead his party's uphill battle to win general elections on October 14 as the party lags in opinion polls, criticised by opponents over rising prices, poverty and crime rates.

"The Labour Party caucus will meet at 1pm on Sunday to endorse the nomination and confirm Chris Hipkins as Party Leader," said a statement by senior Labour Party member Duncan Webb.

As leader of the governing party, Hipkins will also become prime minister when Ardern steps down.

Ardern, a global figurehead for progressive politics, stunned New Zealand when announcing her abrupt exit from office, less than three years after securing a second term in a landslide election win.

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".

'Tough and capable'

Ardern said her decision to step down was "tinged with sadness" but after having made the announcement she had "slept well for the first time in a long time".

Political commentators have lined up to condemn the social media abuse that was increasingly directed at Ardern before her resignation.

Former New Zealand prime minister Helen Clark said Ardern had "faced a level of hatred and vitriol" that was "unprecedented in our country".

Her successor is widely seen as a safe pair of hands with more than 14 years in parliament.

Political commentator Josie Pagani has described Hipkins as "sensible, likeable, tough and capable".

There was no immediate reaction to Hipkins' win from the country's main opposition National Party.

The right-wing ACT Party urged him to "deliver on substance instead of snowing New Zealand with spin", criticising his party's record on the number of welfare recipients, rising food prices and a tight labour market.

The Green Party said it looked forward to working with him to "end poverty, take bold climate action and protect our native wildlife".

Hipkins' appointment also quashed speculation that Justice Minister Kiri Allan, one of Labour's senior Maori MPs, might have become the country's first Maori prime minister.

'Incredibly strong'

But Allan praised Hipkins as decisive and said she believed he would be "an incredibly strong prime minister".

Hipkins won plaudits for his near two-year term as the Covid response minister in a country that shut down its borders to keep the coronavirus out, only fully reopening in August last year.

He conceded last year that people were fed up with the strict pandemic restrictions, describing the border closures as "tough going".

On a lighter note, Hipkins made an infamous slip of the tongue in 2021 when he remarked that virus restrictions made it tough for Kiwis to "go out and spread their legs", instead of stretching them.

Hipkins describes himself as an "outdoor enthusiast" keen on mountain biking, hiking and swimming.