The fire at Islington substation in Christchurch is now out with no one injured.
Smoke was seen billowing across the west side of the city after the oil from one capacitor caught on fire around 1:30pm today.
Eight fire crews battled the blaze with foam, a fire spokesperson says. The fire was in a secure area that fire fighters contained quickly.
It is not known what caused the fire yet.
Roberts Rd is closed between Brunner St and Pound Rd. Traffic is advised to use Buchannans Rd as an alternate route.
The fire service is handing over the operation to Transpower and slowly finishing up at the substation.
Smoke seen from a distance (Annabelle Tukia)
View from offices near the substation (Kevin O'Kane)