The Fire Service describes explosions on an overbridge in Manurewa, Auckland, as quite spectacular.
A power cable fault cut power to homes and brought some trains to a halt at about 6.45am.
The Fire Service says the explosions were caused by a failed 11KV cable underneath the Weymouth Road overbridge.
Manurewa station manager Jeremy Hull says they were about 10 metres high.
Vector is investigating the fault, which caused power to go out in almost 2000 houses for about two hours.
All train services using the track beneath the overbridge are now back to normal.