New Zealand's ruling Labour Party chose former COVID minister Chris Hipkins on Sunday to replace the charismatic Jacinda Ardern as its new leader, and become the next prime minister of the country.

Hipkins, 44, was the only nomination for the job and his confirmation at a party meeting on Sunday, known as the Labour caucus, was largely a formality.

His appointment to the top job followed the surprise resignation on Thursday by Ardern, who said she had "no more in the tank" to lead the country.

"This is the biggest privilege and biggest responsibility of my life," Hipkins said at a news conference announcing his appointment. "I am energised and excited by the challenge that lies ahead."

Known as "Chippy", Hipkins built a reputation for competence in tackling COVID-19 and was a troubleshooter for Ardern when other cabinet ministers were struggling.

Before Hipkins becomes prime minister, Ardern will tender her resignation to King Charles' representative in New Zealand, Governor General Cindy Kiro. Kiro is to appoint Hipkins to the role and he will be sworn in. Hipkins said he will be sworn in on Wednesday.