Nearly 100,000 people spent the day without electricity in Northland after a transmission tower linking the region to the rest of the country collapsed.   

Power was restored to most of the region yesterday evening, but consumers were asked to conserve electricity and warned their hot water cylinders would remain off while the amount of energy getting into the area was limited.   

The tower was undergoing maintenance work when it fell yesterday morning but questions remain on the cause of the collapse.   

The country’s grid provider Transpower issued a grid emergency notice. It was the second such notice issued this year after there was a shortage of generation during a cold snap in May and a solar storm two days later.   

Transpower says they don't yet know why a transmission tower toppled over at Glorit, northwest of Auckland, causing a widespread power outage in Northland.  

NorthPower says supply's been restored to most of the very north of the country while Top Energy's showing 61 customers in Bay of Islands still without.  

But hot water controls are in place, further outages are possible today, and people are urged to conserve power.  

Transpower chief executive Alison Andrew told Mike Hosking that they haven't done a debrief with the crew on-site at the tower.  

She says at the moment they are focussed on restoration, and there will be an investigation, but speculation is unhelpful. 

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• Why did tower fall? Probe launched into region's mass power failure