A fault that has cut power to more than 1600 properties in Lyttelton might not be fixed until tonight.
The outage in the overhead lines servicing the area happened about 3.30am.
Power company Orion said the fault might not be fixed until 8pm.
Orion chief executive Rob Jamieson said operators and contractors were working hard to restore power as quickly as possible.
He said restoring power to businesses and residents in the area in a safe and timely manner was the company's key priority.
However, the job was difficult because of the terrain.
Power is off in Cass Bay, Corsair Bay, Governors Bay, Lyttelton, Pigeon Bay and Rapaki.