They were working to find the cause and restore supply, but it was not yet known when the station would begin generating power again.
In the meantime, reserve generation had been brought online to allow retailers to restore electricity to customers.
Transpower said power had been restored to 90 per cent of customers and companies were working hard to restore electricity to the rest.
"Technicians are working at Huntly to locate the cause of the outage. Huntly remains offline at this stage but there is sufficient reserve generation to meet demand.''
Auckland supplier Vector said most Auckland customers now had power after electricity was restored from about 1.15pm.
In the Wellington region, electricity has been restored to most customers after outages in the lower and central Hutt Valley, Petone, and suburbs including Hataitai and Karori.
In the central and lower North Island, about 30 per cent of Powerco's network was down, affecting parts of Manawatu, Wanganui and South Taranaki.
Power outages were also reported in Bay of Plenty, Gisborne and Hawke's Bay.