A Fire and Emergency Services spokesperson says four crews attended a switchboard fire at the substation.
The fire has now been extinguished.
"At about 3.25pm this afternoon, emergency services were advised of smoke coming from a switchboard room at Vector's Mt Wellington zone substation.
"Firefighters have since contained the area and Vector's response crew are now able to assess the situation," the Vector spokesperson said.
The outages include traffic lights, and Auckland Transport says affected motorists should follow give-way rules, and take extra care.
Vector response crews are on the scene currently and are working on back-feeding electricity to the area from nearby power sources.
Vector are confident the power will be fully restored within the next few hours.