Lines company Powerco says 2300 customers in Whanganui and South Taranaki will remain without power overnight on Monday.
About 600 overhead lines were brought down and a large number of poles damaged in the regions in a storm that lashed most of the North Island at the weekend.
Whanganui and South Taranaki bore the brunt of the bad weather.
Powerco's general manager electricity Andrew McLeod says repair crews will work through the night and major construction projects will resume on Tuesday morning.
Mr McLeod says the damage to the network is the worst Powerco has experienced and customers in rural isolated areas may be without power for another four or five days.
Mr McLeod says crews are discovering that the electricity infrastructure has been wiped out in some areas.
Mr McLeod says many of the customers affected receive power directly from assets that are pretty badly damaged or broken, and there is no other way of getting power to them.
"The only real long-term solution for them is for us to get in there, rebuild the stuff - in a lot of cases from scratch - and get them back on power. So it is a time-consuming process."
Resources are being brought in from around the country to the hardest-hit areas, he says.
Problems for farmers
The power cuts are causing problems not just for farmers trying to milk, but for reticulating water for livestock in Southern Taranaki and Whanganui.
The South Taranaki District Council, Fonterra and and Dairy New Zealand are co-ordinating efforts to get help to farmers - some of whom will have to rely on generators to get their cows milked for at least two more days.
Federated Farmers Taranaki dairy section chair Derek Gibson says significant areas are without power south of Hawera down to Waitotara and some farmers can't get water pumped to stock.
Mr Gibson says more than 20 farmers are booked in for water deliveries on Monday and Tuesday, and expects more to come from isolated pockets where power is out.
Water restrictions remain in place in Whanganui after power was cut to the city's pumping stations.
Whanganui mayor Annette Main says power has been restored to the bores but it will take some time for reservoirs to get to the necessary levels.
While the water may be discoloured, it has been treated and is perfectly safe, she says.