Parliamentary Services says power is returning to Wellington city after an outage knocked out electricity at the Beehive.

An email has been sent out confirming power returning to the precinct and the city.

"However, we cannot confirm the stability of this," it said.

But staff are being told to go home for the day, as well as treasury staff.

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People were temporarily trapped in lifts when the power went out shortly after midday, but they were freed soon after.

More than 10,000 people were affected by the power cut, which was caused by a "zone sub outage" according to Wellington Electricity.

Parts of the parliamentary precinct were plunged into darkness, although other areas were unaffected.

The power knocked out the Radio New Zealand website.

Some staff, taking advantage of their inability to work, went to Copperfield's cafe for lunch, where they were allowed to pay by IOU because the tills weren't working.

It's understood the power was also out at the Wellington courts and the train station.

Power was also out at Victoria University and some lectures have been cancelled.

Wellington Electricity's outage site shows it is spread over multiple suburbs, and that power was expected to be restored within three hours.

A spokesman said the outage was caused by a fault in the Transpower network that supplies Wellington Electricity's.

A message on the Transpower site said there was a fault at the Wilton substation, and there were people on site diagnosing the problem.

The outage happened about 12.15pm.

A Twitter user shared a photo on the site, saying, "Power outage in Wellington CBD. In unrelated news there's a lot of smoke pouring out of the Beehive."

People commenting on the post said the smoke was Parliament's back-up diesel generators kicking in.