New Zealand's Prime Minister Jacinda Ardern has become the second elected leader to give birth while in office nearly three decades after Benazir Bhutto did in 1990 as the then prime minister of Pakistan.

Ardern announced the birth of her daughter in Auckland last week and set an example of being a woman who could not only run a country but also be a mother, simultaneously.

The 37-year-old has taken six weeks of maternity leave, and has passed on her duties to Deputy Prime Minister Winston Peters. However, she said she would be consulted on significant issues and would continue to read cabinet papers during her time away.

In 1990, Benazir Bhutto gave birth to a daughter while serving as Pakistan's prime minister, a first for an elected world leader. Incidentally, Ms Ardern's baby was born on what would have been Ms Bhutto's birthday.