Power is out in West Auckland's LynnMall and some nearby homes in the suburb of New Lynn.
A Vector spokeswoman said the number of people affected was "reasonably small".
"The outage is a result of a fault to the lines. Crews are on site, and the majority of customers have now had their power restored," she said.
"We estimate that power will be fully restored by 10pm."
Countdown LynnMall checkout supervisor Parveen Sharma said the power went off soon after 6pm but the store continued trading using emergency backup.
"It's affected about half of the mall," he said.
Surrounding businesses said they had not been affected.
Vector said customers could keep up to date as power is restored through the Vector Outage Centre, available on vector.co.nz/outages.