A Watercare worker has suffered minor burns to his face and arms while investigating a wastewater pipe in Remuera.
A Watercare spokeswoman said a pipe blocked by tree roots was being repaired at the time.
Several Watercare workers were breaking open concrete surrounding a pipeline and struck a live electrical cable at midday in Ladies Mile.
That caused a flash and led to the worker suffering minor burns. He was taken to Middlemore Hospital but is expected to be discharged this afternoon.
WorkSafe has been notified and Watercare has begun an investigation as to the cause of the accident.
The site remains cordoned off. Traffic is flowing normally.
Watercare infrastructure delivery manager Steve Webster said the worker's family had been told about the incident.
"The crew were not underground at the time. They were working in a shallow excavation in the berm when the incident occurred."
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The Fire Service tweeted that the explosion was caused by electrical wiring.
A St John spokeswoman said one person was treated at the scene for burned arms.
Four fire crews attended and the Fire Service urged people to avoid the area.
Cordons were put in place at Ladies Mile and Remuera Rd.
The Fire Service urged people to avoid the Ladies Mile area.