"Welcome to our village wee one," Ardern wrote on Instagram at 6.15pm on Thursday.
New mums and a stay-at-home dad have offered valuable advice to soon-to-be parents, Prime Minister Jacinda Ardern and partner Clarke Gayford.
Ardern and Gayford remain in Auckland Hospital after arriving just before 6am. There will be no further announcements until their baby is born.
Gayford drove them to hospital in their own car as planned.
The PM's office has passed on information from Auckland DHB that 16 babies have been born at Auckland Hospital so far today - there is no indication of whether the Prime Minister's is one of them.
A group of about 25 parents with their babies and toddlers took part in the weekly 'wriggle and rhyme' class held at Mt Albert Library today.
After half an hour of dancing, clapping and belting out well-known nursery rhymes, the Herald spoke to a number of parents about what advice they had for Jacinda and Clarke.
One mother said, "Take people's help when they offer it." While another said, "Take your time and mess can wait."
Another mother added, don't take "too much advice, listen to your own intuition".
Watch: New parents offer advice to Jacinda and Clarke ahead of baby's arrival
"I think it's really progressive, it sends a really good message to other dads around the country," a mother said.
"As long as you get the bottles and expressing routines sorted, should be good to go."
One stay-at-home father suggested Clarke up his caffeine intake to get through and also to get used to sleepless nights ahead.
Governor-General Dame Patsy Reddy posted this photo on Facebook, saying "A rainbow today at Government House, perhaps suggesting glad tidings are imminent".
A rainbow today at Government House, perhaps suggesting glad tidings are imminent.
Meanwhile, Acting Prime Minister Winston Peters is keen to create the impression that it's business as usual for the Government.
Speaking to reporters as he headed into Parliament, Peters downplayed suggestions today was a historic day.
"If you've been around as long as I have nothing is unusual at all," he said.
Peters confirmed he had been in contact with Ardern today by text message, but would not say when.
Asked to explain the extra responsibilities he was taking on in the top role, he said: "I'm taking on all the duties of the prime minister and getting on with the job, without getting carried away by it all."
However, Leader of the Opposition Simon Bridges acknowledged the occasion was special, joking he felt starved of political oxygen given the media and national interest in the Prime Minister's baby.
"A beautiful baby will be a real blessing for (Jacinda) and Clarke, it will give them many years of joy," he told The Country today.
Bridges said he doesn't "get silly about" or overly "distracted" by the potential negatives on his children: "it just means you put a few protections in place".
"We are fortunate that we live in Tauranga, it would be somewhat harder in an Auckland or a Wellington," he said.
"And we've been there for a long time, people know us, they know who we are and we just try and no-nonsense get on with it."
Ardern, 37, will become just the second prime minister to have a child while in office.
When former Pakistan Prime Minister Benazir Bhutto gave birth to her daughter Bakhtawar on January, 25, 1990 she was the first modern head of government to give birth while in office. Bhutto was assassinated in 2007.
As coincidence would have it today would have been her 55th birthday.
Ardern's arrival has sent ripples of excitement around the hospital.
A doctor who works there says she heard about Ardern going into hospital on the radio.
She says she's excited for the Prime Minister and hopes she gets out of hospital soon.
A nurse who had just finished a night shift thought it was interesting that the Prime Minister was giving birth at the hospital amid all the controversy of industrial action.
She says it's exciting all the same and is wishing Ardern all the best.
Another man, who arrived at the hospital to visit a sick grandchild, said he was excited to know if Ardern would have a boy or a girl and wished her well.
There will be no further formal announcements from the Prime Minister's office until Ardern and Gayford, 40, announce the birth of their baby.
Auckland City Hospital says 6974 babies were born there last year.
"The average length of stay for a woman giving birth in our hospital is 2.3 days. Typically a woman will be discharged home or to Birthcare, depending on her requirements."
If born today Ardern and Gayford's baby would share a birthday with Prince William (who the couple met in Britain this year), actor Chris Pratt and singer Lana Del Rey. Their star sign is Cancer.
The irony that if anti-monarchist Jacinda Ardern's baby is born today, her child will share its birthday with the future King of England (and New Zealand). 👑🇬🇧🇳🇿😲🍼 #nzpol
The child's birth will be significant; given he or she is the first child born to a female New Zealand Prime Minister, in power, in our country's history.
Reckon #HilaryBarry might win Jacinda’s baby bet - today/boy
Prince William, 1982 Joko Widodo, Indonesia president, 1961 Lana Del Rey, musician, 1985 Edward Snowden, NSA whistleblower, 1983 Jean-Paul Sartre, French philosopher, 1905 Benazir Bhutto, former Pakistan prime minister and first female leader of a Muslim nation (also the first head of government to give birth while in office), 1953 Shirin Ebadi, Iranian lawyer and human rights activist and first Muslim woman to receive the Nobel Peace Prize (2003), 1947
"This is an exciting time for Jacinda and Clarke and a historic moment for our country," said James Shaw in reference to the fact that this will be the first time a Prime Minister in New Zealand has had a baby while in power.
"I join with Marama and our Green Party caucus colleagues in wishing them both all the best."
How the baby news was announced
In mid-January, Ardern shocked the country when she announced, via social media, that she was expecting.
"We thought 2017 was a big year. This year, we'll join the many parents who wear two hats. I'll be PM & a mum while Clarke will 'first man of fishing' & stay-at-home dad," the couple announced.
"There will be lots of questions [I can assure you we have a plan all ready to go] but for now bring on 2018.''
We thought 2017 was a big year! This year we’ll join the many parents who wear two hats. I’ll be PM & a mum while Clarke will be “first man of fishing” & stay at home dad. There will be lots of questions (I can assure you we have a plan all ready to go!) but for now bring on 2018 pic.twitter.com/nowAYOhAbF
It was also a nice touch given the significance of the hook in Māori culture.
It was later revealed she planned to take six weeks off after the birth - of which a due date of June 17 was given.
There was great support from the New Zealand public, political colleagues and from fans around the world.
Australian Prime Minister Malcolm Turnbull was one of the first international leaders to tweet about the news.
"Congratulations Jacinda Ardern on your wonderful news today. When we spoke this morning you sounded more excited than you did when you won the election!"
Congratulations @jacindaardern on your wonderful news today. When we spoke this morning you sounded more excited than you did when you won the election! Lots of love and best wishes from me and Lucy and all of us across the ditch.
Some eagle-eyed Kiwis were quick to point out that now meant Clark was very much the real "aunty Helen".
Wishing @jacindaardern & @NZClarke all the best as they expect their 1st child in June: a super busy year coming up & much to look forward to. Every #woman should have the choice of combining family & career. https://t.co/Ma6B6OGXJe
Ardern has been well received at public events during her pregnancy and has travelled and appeared at many engagements over the past few months.
Her trip to Waitangi, in the lead-up to Waitangi Day, was widely regarded as one of the best appearances of any New Zealand leader in history.
She became the first female prime minister to speak at the upper marae and many remembered her walking around in barefoot and helping to serve the public a hearty breakfast alongside her Labour Party colleagues.
She toured the Pacific this year and later Europe, where she and Gayford met the Queen.
