Power is out in the Auckland suburb of Hillsborough after locals reported hearing a loud bang.
Electricity company Vector says power may be out for some time as it investigates the cause.
"Vector is responding to an outage affecting customers near the corner of Mt Albert and St Andrews roads in Hillsborough," a spokeswoman said.
"Vector's electricity operations centre has remotely redirected power flows to as many affected customers as possible, and our crews are currently on site investigating. At this stage, it is believed that the cause may be a possible feeder fault."
Customers in the area should prepare to be without power "for some time", she said.
Crews aimed to respond as quickly as possible while ensuring the safety of workers and the public.
People can keep up to date with restoration work relevant to their specific address through the Vector Outage Centre, available on vector.co.nz/outages.
The company reminded people to stay away from damaged electrical equipment and report issues by calling 0508 VECTOR.