Civil Defence in Wanganui says the town's water supply is under threat after Saturday's wild weather damaged power lines to the Kai Iwi pumping stations.
Wanganui Mayor Annette Main says Powerco is working as fast as possible to repair the lines to the town's water pumping stations but in the meantime residents must use as little water as they can.
Powerco says 16,000 of its customers are without power overnight in south Taranaki and Wanganui.
Powerco general manager Andrew McLeod says field staff will be working through the night and on Sunday to restore power as quickly as possible.
But he says it may up to five days before power can be restored to customers where access is difficult or damage is extensive.
Mr McLeod says the storm had caused trees and branches to break, bringing down many poles and overhead lines.
He says there are currently 350 lines down in South Taranaki alone, and a further 250 in Wanganui.
Meanwhile, in Upper Hutt power was restored to around 150 homes on Saturday evening.
Vector says 270 of its customers in Piha and Kaipara have had their power restored, although linesmen are still working to connect about 120 properties in Takatu near Warkworth.
Severe weather eases
MetService has relaxed its severe weather warning, saying severe gale-force winds across Wellington, Marlborough and eastern parts of the North Island will ease on Saturday evening.
MetService predicts a ridge of high pressure moving onto the country on Sunday.
The Fire Service says 265 people called for assistance in Wellington on Saturday morning.
Shift manager Murray Dunbar says firefighters were sent to 215 of those calls. The others were referred to agencies like power companies and the police.
One firefighter who was called to Wainuiomata to remove a fallen tree from the roof of a house, was injured when the tree struck her. She is in hospital.
Interisland ferry crossings are cancelled for Saturday. There were also disruptions to services at Wellington, Napier and New Plymouth airports.
Police report some houses in Patea had roofs blown off and windows smashed.
The Ironman New Zealand race in Taupo was cancelled.
No post in Wellington
The Postal Workers Union said its members did not deliver mail in Wellington on Saturday because of the storm.
The union represents a number of posties in the Wellington area, but not all.
New Zealand Post confirmed some of its services had been cancelled.