The majority of customers impacted by an outage in the West Auckland area last night had their electricity restored at 11pm.
Approximately 1,000 customers in the Konini area are still without electricity, and crews are working to restore supply to these customers, lines company Vector said.
Crews restored customers in Henderson Valley, most parts of Rosebank and the MacLeods Road area at 8.45pm.
At the height of the outage, some 10,000 houses were without power after the Hepburn Rd substation failed about 7.15pm.
Crews from Vector and Transpower were yet to find out why the substation failed.