A forklift carrying a shipping container was responsible for a major power blackout which affected the top of the North Island on Friday.
National grid operator Transpower says a circuit on the 220kV line from Otahuhu to Henderson tripped just after 8am while the other circuit was out for maintenance.
The result was a loss of power to Northland and parts of Auckland north of the Harbour Bridge, affecting about 280,000 consumers.
The Marsden Point oil refinery was put into an emergency shutdown and spokesman Ken Rivers says the shutdown will cost hundreds of thousands of dollars. But he says the main concern was the potential disruption to supply.
Dairy farmers also want security of supply to make sure a day's milk doesn't end up down the drain.
Dennis Anderson of Federated Farmers, Northland, says most farmers consider themselves pretty lucky to have got the cows in and milked before the power cut.
All power to Auckland and Northland was restored at around 11am.
The Fire Service's Northern Communications centre says two people got stuck in elevators on the North Shore but were quickly freed.
The power outage also caused headaches for the High Court and District Court in Whangarei when the computer system went down, meaning no cases could be processed.
Transpower spokeswoman Rebecca Wilson says investigations showed the forklift carrying a container hit the overhead line near Otahuhu.
Transpower has always been concerned about the "underbuild" which allows companies to operate under high-voltage power lines, she says.
"We do have a corridor management policy which does not allow that now within certain safety areas," she says.
There are guidelines but the "underbuild" issue goes back years to when industry was allowed to build under power lines. Wilson says the forklift was carrying a "massive" container when it hit the line.
The cable will be repaired as quickly as possible while the other line is providing power.