About 85,000 homes - tens of thousands of people - in Remuera, Epsom, Ellerslie and Mt Wellington were without power and traffic lights were also affected, power company Vector said.
By late this afternoon, Vector crews have managed to restore several Auckland suburbs.
So far Epsom, Penrose, Te Papa and Rockfield are back online, the lines company advised this afternoon.
"This brings the total number of customers out down to 53,100, down from the 85,000 out at the height of the substation fire this morning," Vector said.
Crews are currently working on restoring Newmarket, with power in Westfield likely to be back on between 6pm and 8pm today.
"It's hoped Glenn Innes will also be restored later this evening. The total number of customers we hope to restore this evening in this group is 13,500," Vector said.
Those in Sylvia Park, Remuera, Mt Wellington, St Johns, Orakei and St Heliers - suburbs affected by the damaged cables - should prepare for a night without power, with Vector expecting those suburbs to be offline until tomorrow.
"Crews would continue overnight and throughout tomorrow in order to get customers restored as soon as possible," Vector said.
Mobile phone service for Vodafone, Spark and 2degrees customers in Auckland has been badly affected by today's power outage.
About 160 cell sites are in the affected region and all were running on battery back-up, which was now running out, the companies said.
Some suburbs could be without power for up to two days, an update on Vector's website said.
The company's "best estimate" at this early stage was that the suburbs that were likely to be out of power for up to 24-48 hours were: St Johns, Remuera, Sylvia Park and Mt Wellington, the update said.
Medically dependent customers or vulnerable customers in these areas should make alternative arrangements, the company said.
"If all goes to plan, there may be some restoration in the peripheral areas of these suburbs that could take place earlier, if the crews can back feed, although that is difficult to establish at this early stage."
Auckland's Civil Defence Centre has been activated to help manage the impact of the power outage.
Civil Defence controller Clive Manley said his priority was to provide assistance to those who were in most need and ensure that critical infrastructure continued to operate.
"We are in close contact with Vector, Transpower, police and the Fire Service."
A Vector spokeswoman said reports by some households of losing power at 11pm last night were not related to this power outage.
An initial investigation had revealed substantial damage to a number of cables feeding some eastern, central and southern suburbs, it said.
"Vector mobilised extra resources when news came through of the fire early this morning and will get to work on repairing these damaged cables now.
"It's expected that the crews will work through the night to effect these repairs, but this will take some time.
"Every cable and every piece of switchgear must be thoroughly checked before being re-livened, so an initial restore to some areas might still take some time."
