Authorities warn the powerful storm could cause coastal flooding and landslides.
Vaianu, forecast to bring heavy rain and winds of up to 130km/h was expected to hit on Sunday, then pass west of the remote Chatham Islands on Monday, weather forecaster MetService said on Saturday.
Several regions were under emergency declarations on Saturday, with authorities ordering evacuations in some parts of Whakatane, population 37,150, about 430km north of the capital Wellington.
"Residents should plan to be away for at least two days," the Whakatane District Council posted on Facebook.
On coastal areas, the storm could cause landslides, storm surges, waves of up to 13m and coastal flooding, it said.
Prime Minister Christopher Luxon on Friday said the cyclone had the potential to be damaging and urged those in its path to prepare for impact.
"Make sure drains are free, check in on the neighbours, and be prepared for possible power cuts," Luxon said on X.
Vaianu has conjured up the painful memory of 2023's Cyclone Gabrielle, which killed 11 people and displaced thousands in New Zealand's biggest natural disaster this century.
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