Many homes and businesses in Northland are without power after a Transpower tower fell near Kumeū about 11am.
The crisis arose after Northpower lost a major high voltage line into the substation at Maungatapere, a major feed from the grid, which caused much of the region to lose its supply.
A Transpower service provider was on site to assess the damage and determine an expected time when power could be restored.
While no time has been announced yet, some areas are now running on backup generator, however, Transpower said power needed to be conserved until normal supply is up and running.
By mid-afternoon Transpower said power had been partially restored and some people have already been reconnected. It was not clear how many people this affected.
"Transpower is restoring as much capacity as possible through its lower capacity 110 kV network. However, until one of the larger 220 kV circuits is returned to service there will be insufficient electricity available to fully power the region," the national grid operator said.
A sign on the door of a business in Northland. – RNZ/Peter de Graaf
Transpower was able to reconfigure the power system to provide power including from local sources, such as the geothermal generation at Ngāwhā.
The tower fell while a second transmission circuit supplying these areas was out of service for scheduled maintenance.
Transpower was also assessing how long it would take to return that circuit to service.
Whangārei mayor Vince Cocurullo said it was probably the largest one-off outage that he's seen in "a long, long time".
"This has taken the whole of Northland out," Cocurullo said.
Northland Police asked the community to be patient on the roads and to take care at intersections.
Police were managing traffic on the main roads, and at intersections where traffic lights, a spokesperson said.
"There will be a visible police presence in our business areas across the Northland District.
"We ask motorists to only travel if necessary and the best practice is to stay off the roads to stay safe."