Just before 7pm, the properties in Napier and Hastings reported a loss of electricity, leaving the cities in darkness.
Transpower said it appeared a cat sneaked into Redclyffe substation, making contact with the equipment, causing an explosion.
It said when crews arrived at the substation, they found a cat's remains.
Earlier in the evening Transpower apologised and thanked consumers for their patience.
"Supply has now been restored to Redclyffe substation, it may take a little time to come back on at homes and businesses in the region."
Power has now been restored throughout the region.