Large parts of North Auckland without power since Wednesday morning may have services restored about midnight, Vector says.
A map on the Vector website shows the outage affecting areas across the Kaipara Flats, up to Wellsford and to Omaha in the east.
Western parts of Kawau Island are also in the dark.
Vector said the outage was due to an equipment fault and it had a team resolving the issue.
The map's updates history shows that Vector received reports of an outage in the region just before 8am on Wednesday.