Seven local council areas, including the South Island's main city of Christchurch, declared a state of emergency on Tuesday as officials anticipated the worst.
Air New Zealand cancelled all flights into Wellington and four other airports through to midnight on Tuesday as roads were closed around the coastal town of Kaikoura and schools in the upper half of the South Island closed ahead of the storm's arrival.
Garry Howard, mayor of Buller, said the storm is expected to hit the district tonight (local time) - it is now 9pm in New Zealand, as the country is 13 hours ahead of GMT.
Tens of thousands were without power on Tuesday night as locals were warned to prepare for floods, huge waves and gusts of winds reaching close to 200km/h.
The full force of Cyclone Gita hit Tonga with 275 kph winds last week causing extensive damage.
'We are expecting homes to be flooded'.
"The high-impact severe weather across central New Zealand should then ease as Gita moves away on Wednesday", a MetService forecast said.
Gita then skirted the south of New Caledonia, but caused no major damage, before curving to the south and running towards the land of the long white cloud. "Granity in particular has high seas predicted and along with high winds this is not a good situation for those in seafront properties".
Prime Minister Jacinda Ardern said earlier that troops had also been sent out to areas that were likely to be hardest hit by the storm.