Drivers revert to give way rules in Wellington CBD after a power cut causes traffic lights to be out of order.

As much of Wellington went into black-out, firefighters had to switch to an old-school back-up to keep in touch with base.

The cause of the massive outage - that affected 12,500 properties in multiple suburbs, as well as Parliament, parts of Victoria University, city courts and businesses - has been blamed on the failure of a piece of equipment at Wellington's Wilton substation.

The outage began at 12.15pm on Friday. Power was restored across Wellington by 3.17pm.

Jessica Long / Stuff Homes and businesses across Wellington suffer due to major power outage.

Lectures at Victoria University's Rutherford House were cancelled and Wellington District Court was halted when the power went out.

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WENDY MURDOCH/STUFF At the corner of Bowen St and Lambton Quay traffic was stalled as the lights went out.

The entire parliamentary precinct, including both Parliament House and the Beehive, was plunged into semi-darkness.

Properties in the northern end of the CBD and surrounding suburbs, stretching north to Khandallah and west to Karori were also affected.

A Fire and Emergency spokesman confirmed that the central region's digital "Selcal" system - a digital form of communication between on-the-ground crews and central communications - was down for 25 minutes on Friday, from 12.20pm to 12.45pm.

WENDY MURDOCH/STUFF Traffic negotiates and intersection without lights.

While the power outage was the most-likely culprit, that was not yet confirmed and Fire and Emergency would look into the cause.

New Zealand Professional Firefighters' Union Vice-President Ian Wright said the contingency was for a return to the old, slower way of talking on radios.



"We understand technology can fail."



This slowed the process down at a time a lot of calls were coming in - largely because back-up diesel generators in offices around town were fired up, causing a lot of smoke.



A Fire and Emergency spokesman said a couple of people were trapped in lifts when power first went out but they had since got out.

Transpower said: "We've been able to identify that the equipment that connects two sections of the power system together at the Wilton substation has faulted.

WENDY MURDOCH/STUFF Lights out the the corner of Molesworth St, outside Parliament as a major power outage hits Wellington.

"But, as designed, the protection mechanism actually kicked in to ensure the network is not damaged.

Transpower would review the issue for "any lessons learned".

The Buzz Cafe assistant Anna Mei said it was her first day on the job. She closed the cafe when the power went out just after midday.

"[The owner] says we lost almost $600 to $700 today because Friday is the biggest income day. We need to afford staff."