Extra crews have been brought in to restore power to more than 15,700 homes in hard-hit Taranaki in Gita's wake.
Gale-force winds gusting above 130km/h knocked out power for more than 20,000 homes in the region last night, when local officials declared a state of emergency.
Powerco network operations manager Phil Marsh said Taranaki and Whanganui were hardest hit and extra crews have been brought in to repair the network.
"We have suffered considerable damage with downed lines a major problem in coastal Taranaki," he said.
"We were able to restore power to about 10,000 people overnight. At the height of the storm there were about 26,000 without power."
He could not predict when power would be restored to everyone.
"Thankfully conditions have calmed down but the damage is spread right around the mountain in Taranaki with faults in almost 30 different areas. Lines, transformers and poles had all been affected.
At 7am Powerco customers still off line were spread across Taranaki (13,224), Wanganui (2103) and Manawatu (422).
"Our biggest concern is downed lines and the need for everyone to treat them as being live. People may find downed lines we have not been told about. They need to call emergency services immediately."
A state of emergency was declared in Taranaki at 7.50pm, one hour after power had been cut to nearly 23,000 homes, Civil Defence said.
A pipeline from the New Plymouth water treatment station to the Mangorei Reservoir was also ruptured by a falling tree.The last time Taranaki experienced such widespread cuts was in November 2016, when 13,000 homes lost power after the Kaikoura earthquake.
That was immediately followed by a storm that caused further damage to the network that took several days to repair.