Prime Minister Jacinda Ardern has been admitted to Auckland Hospital.
Ms Ardern, who is expecting her first child with partner Clarke Gayford, was due to give birth on June 17.
A 6:30am press release from the Prime Minister's office has confirmed that both Ms Ardern and Mr Gayford have arrived at Auckland Hospital.
Deputy Prime Minister Winston Peters will step up to Acting Prime Minister while Ms Ardern is on maternity leave.
Ms Ardern has said she will take six weeks leave before returning to work running the country.
Ms Ardern announced her pregnancy in January, just days after being sworn into office as the Prime Minister of New Zealand.
She had been the leader of the Labour Party for just three months at the time.
Announcing the birth, Ms Ardern said the couple were excited to be "joining the many parents out there who wear two hats".
"I'll be Prime Minister and a mum, and Clarke will be 'first man of fishing' and stay-at-home dad," she said.
"I think it's fair to say that this will be a wee one that a village will raise, but we couldn't be more excited."
She is only the second world leader in history to give birth while in office. Pakistan's former Prime Minister Benazir Bhutto gave birth to a daughter in 1990.