Jacinda Ardern has officially become the new prime minister, being sworn in by the Governor-General.

History has been made as Jacinda Ardern takes the reins as New Zealand's 40th Prime Minister, and the youngest woman to lead the country.

In true Labour style, Ardern and her ministers travelled by bus to Government House in Wellington to be sworn in by Governor-General Dame Patsy Reddy on Thursday morning.

Family, friends and hordes of media gathered inside Parliament House, with Ardern's partner Clarke Gayford, and her father Ross, were front and centre.

Governor-General Dame Patsy Reddy welcomes incoming PM Jacinda Ardern and Deputy PM Winston Peters to the official swearing in.

It was a real family affair, with Gayford's nieces there for what one of them called "Aunty Cinda's lady party". Meanwhile, in the UK her sister Louise gave birth to a boy on the same day.

READ MORE:

* Live: New government sworn in

* Ardern thanks unions for support in first major speech as PM-elect

* English makes final appearance from PM's office

At Government House, the 37-year-old Prime Minister was the first to walk the red carpet and shake hands with Reddy on the dais, beneath a portrait of the Queen.

MONIQUE FORD/STUFF Jacinda Ardern's partner Clarke Gayford stands in the audience as she is sworn in as prime minister.

She'd already been the Prime Minister-designate for a week but this was the day history was made, and that sense of history being made was clear among the hushed crowd with beaming faces.

Deputy Prime Minister Winston Peters followed, along with the rest of the ministers and under-secretaries from Labour, NZ First and the Green Party.

They were greeted beneath the Queen's gaze by Reddy and Ardern, before taking their seats at a table that ran the length of the grand room.

MONIQUE FORD/STUFF Prime Minister Jacinda Ardern, her partner Clarke Gayford, and her nieces on the steps of Parliament.

When asked by Reddy, Ardern confirmed she could form a stable government, and was officially sworn in as leader of the executive, to great applause.

She signed her warrant as prime minister, and swore an oath of office ahead of the other ministers.

Many ministers - such as Shane Jones and Kelvin Davis - took their oaths in Māori, and for the first time, Su'a William Sio took the oath in Samoan.

ROBERT KITCHIN/STUFF Prime Minister Jacinda Ardern gets set to lead her first ever Cabinet meeting, after being sworn in.

After Labour's Phil Twyford orally took his oath, Chris Hipkins leaned across and said, "that's going straight to the pool room".

Ministers then signed documents, before a ceremony where ministerial warrants were signed by the Governor-General. Parliamentary under-secretaries were then sworn in.

In total, 14 ministers and under-secretaries took the affirmation of allegiance, instead of swearing on the bible, including Ardern.

STUFF Bill English was farewelled by staff on his way to Government House to hand in his resignation as prime minister.

Meanwhile, 17 did use the bible, including all of NZ First.

Before the new executive broke to have their pictures taken and lunch with the Governor-General, Ardern addressed her new government.

"I expect, but I also know, that all of you will do this job to the best of your abilities," she said.

"We have a responsibility now, to all New Zealanders, to do our very best to achieve the goals of this government. To be a government that is active, that is focussed, that is empathetic, and that is strong."

Following the more sombre, traditional swearing in, the fresh government met the masses with an inauguration-style return to Parliament.

A band — a quarter of Kiwi group Fat Freddy's Drop — and more than 500 supporters gathered at Parliament to welcome the new government. The relaxed, campaign-style welcome was partially Ardern fulfilling her promise to a voter who she'd spoken to online ahead of the election.

The new Prime Minister addressed the crowd, flanked by her ministers, saying it was an " enormous privilege and an honour" to stand before her supporters; "in front of your house, with your government".

"Not everyone voted for us, this is a democracy, of course not everybody voted for us. But we vow that regardless of who you voted for, regardless of where in Aotearoa New Zealand you live, this will be a government for all New Zealanders."

She signed off with a twist on Labour's campaign slogan: "Let's go and do this."

PAYRISE FIT FOR A PM

With the added responsibility, comes a few extra dollars.

Ardern is set for a big payrise as she takes on the top job, while Opposition leader Bill English will receive a paycut.

The salary for the Opposition Leader for the 2018 financial year is $296,007, plus $16,980 in allowances ($312,987).

While the salary for the Prime Minister is $471,049, plus $22,606 in allowances. Taking the total to $493,655.

That means Ardern has snagged a $180,668 payrise, which means English's salary has been slashed by the same amount.

English will also lose some of the perks of the top job, like his security details. But he will keep the Crown limo.

Meanwhile, Ardern has signalled she will be moving into Premier House, the Prime Minister's official residence.

Winston Peters will also receive a payrise as Deputy Prime Minister, to $334,734, plus $16,980 in allowances.

NEW 100-DAY PLAN

Following her public welcome, Ardern addressed the media and said she would outline her new 100-day plan on Tuesday.

There would be a few changes to the plan released before the election, but not many, she said. The new plan would likely include a "mini Budget", and would still include the promise of free tertiary education for the first year, from 2018.

Ardern and her senior ministers then made their way to the Beehive, where she led her first ever Cabinet meeting on the 10th floor.

BILL BIDS FAREWELL

Shortly before the new Prime Minister and her Government were officially sworn in, another resigned.

Earlier on Thursday morning, about 40 staff gathered at the entrance to the Beehive to farewell National leader Bill English, as he set off on his last trip as prime minister.

Bring driven off in Crown Car CR1, he also went to Government House, but this time to hand his resignation to the Governor-General.

English would now be the leader of the Opposition.

Late on Wednesday night, English sent a letter to his supporters saying the final election result was "of course disappointing", but it was important to accept the election result "which is entirely legitimate under MMP".

"The job now is to pick ourselves up and begin the fight again for the values we all believe in."

English was re-elected as leader of the National Party on Tuesday and planned to hold the post until the 2020 election.