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Orion is still looking into what caused power cuts to 30,000 in north Christchurch overnight.
The outage initially affected 30,000 customers, although power was quickly restored to 12,000 homes and power was restored to all within three and a half hours.
Orion chief executive Rob Jamieson said the fault occurred on a high voltage line which runs for 9km from Islington to Papanui.
"Last night, and again at first light this morning, our crews walked the line to try to find the fault and we have found no obvious cause."
They were continuing to investigate what caused the rare type of outage, he said.
Mr Jamieson said the fault, as a result of a storm, was a reminder to people that power failures occurred at any time so it was important to be prepared.
"Everyone needs a back-up plan, which includes having torches, with spare batteries, and a wind up radio. Simple preparations can make a big difference."