Prime Minister Jacinda Ardern is pregnant, but reluctant to be called a trailblazer, saying she's going to be far from the first woman to balance work and children.
Ms Ardern, 37, on Friday announced she and her partner, television presenter Clarke Gayford, were expecting a baby in June, describing it as a "surprise".
Deputy Prime Minister Winston Peters will take on the top job for six weeks after the baby is born.
"He's played that role before. When I go overseas he plays that role. That's not unusual," Ms Ardern told reporters outside her Point Chevalier home.
"After those six weeks I'll be coming back on deck."
While acknowledged she faced a challenge balancing home life and her prime ministerial duties, Ms Ardern was reluctant to paint herself as a trailblazer.
"I am not the first woman to multi-task. I am not the first woman to work and have a baby. I know these are special circumstances but there will be many women who will have done this well before I have," she said.
"I am about to sympathise with them a lot, as I sympathise with all women who suffered morning sickness.
"And New Zealand is going to help us raise our first child."
Ms Ardern received the news on October 13 and became prime minister six days later.
The couple had earlier been told they would need help conceiving and had stopped getting assistance when Ms Ardern became Labour leader last August, she said.
Mr Gayford will be primary carer and will travel with her as much as possible. He wasn't being drawn on the question of a marriage.
He said he liked the idea they were doing everything in reverse, they bought a house together, now they were having a baby and "then we'll see".
She declined to reveal the baby's gender and said no name had been chosen, but said it would likely have Mr Gayford's surname.
Ms Ardern and Mr Gayford received congratulations from across the political spectrum following the announcement - including from former prime ministers Bill English, Helen Clark and Jenny Shipley - and prompted more than 40,000 tweets in the first hour.
Ms Ardern said a call from Australian PM Malcolm Turnbull "was purely a call about kids".
Australian Labor Party leader Bill Shorten tweeted "Wrapped to hear the news from across the ditch this morning" and some people on social media pointed out his spelling mistake.
Ms Ardern is not the first world leader to be pregnant. Pakistan's Benazir Bhutto caused a stir with her second pregnancy in 1990.
Ms Ardern said she had given a heads-up to Governor-General Dame Patsy Reddy and she would attend the Commonwealth Heads of Government Meeting in the UK in April.
Ms Ardern said she had had pretty bad morning sickness for three months.
She hopes the baby will be born in Auckland where the couple live but will prepare for scenarios as parliament is based in Wellington.
Massey University Associate Professor Grant Duncan said there was no reason why the pregnancy of the prime minister should in itself create any significant constitutional or political problems.
"Instead, I see this as a great opportunity to show by example how we can support parenthood and family, and to show the world that New Zealand is leading the cause of gender equality."