A state of emergency has been declared in parts of the South Island and in Taranaki as former cyclone Gita makes landfall, bringing heavy rain and high winds.
In Taranaki, nearly 23,000 properties were without power early on Tuesday evening as gusts reached 140km/h.
Some power consumers have been told they might remain disconnected overnight and into Wednesday.
There have also been calls to conserve water in eastern parts of New Plymouth District after a fallen tree ruptured the pipeline from the city's water treatment station to the Mangorei Reservoir.
Buller, Tasman, Grey, Westland and Selwyn districts and Christchurch city have also declared a state of emergency, with forecasters predicting that the worst of the weather is still to come.
Westland Civil Defence controller Simon Bastion says there have been reports of trees down and damage to buildings and people are urged to avoid all travel unless urgent.
Damaging gale-force southeast winds are hitting the area from Hari Hari to Fox Glacier, and Franz Josef medical centre has been turned into accommodation for tourists for the night.
Christchurch mayor Lianne Dalziel says her council made the declaration in the afternoon to give people plenty of early warning to prepare.
"The full impact of the storm will be felt overnight and tomorrow morning," Ms Dalziel said.
"We are expecting homes to be flooded."
She said people in flood-prone areas, especially those affected by last July's storm, should consider evacuation.
Buller mayor Garry Howard says Gita's effect on his district is expected to be greatest during darkness.
"Granity in particular has high seas predicted and, along with high winds, this is not a good situation for those in seafront properties," he said.
Nelson Tasman Civil Defence has reported an increasing number of incidents and significant flooding in the Riwaka Plains.
The Salvation Army Hall in Nelson has been set up as a centre where people can self-evacuate to if concerned for their safety.
Meanwhile, Gita has also forced flights to be cancelled and roads closed, including State Highway 1 north and south of Kaikoura, and the inland route (Route 70) out of the district.
More than 40 schools and 17 early learning centres didn't open on Tuesday.