Thousands of Waitaki power consumers fell victim to a once-in-a-decade power cut on Saturday.

Two Transpower transmission circuits feeding into the Network Waitaki lines network tripped about 8.30am, cutting power to about 11,000 connections.

The outage was widespread, including Hampden, Kakanui, much of Oamaru and the rural hinterland inland to Ngapara.

Network Waitaki network general manager Shane Watson said about 80% of its customer base was affected.

The community-owned lines company was able to restore power to "just about half" its customers by 9.15am.

This had been possible through a limited supply via the Waitaki Valley.

"[For us] it was more an operational issue on how we tried to manage and get what limited power supply we had on to try and limit the consequences of the outage.

"Due to the limited nature of that supply, we couldn’t really get any more on until Transpower were able to resupply their lines."

That did not happen until about 10.30am. We had just about everybody on by midday."

Mr Watson said Saturday’s cut was one which might happen once every 10 years.

Transpower grid delivery general manager Mark Ryall said yesterday the transmission company was unsure what had caused the cut.

"We are continuing to investigate our assets in the area in more detail, despite the helicopter patrol crew not finding any signs of cause for the tripping," Mr Ryall said.

"We know in the past birds have caused issues on lines in this area, but there is no evidence yet to show this was the case here."

nic.duff@oamarumail.co.nz