Saturday's storm was still raging when hundreds of people rushed to hire or buy generators and gas cookers, and stock up on candles and matches.
Wanganui Gilbertsons Mitre 10 retail manager Glen Mailman said people were lining up wanting generators when the doors opened at 8am.
"By 10am all our stock was gone, which was about 15 2.5kW generators."
Mr Mailman said the generators cost $500 each.
"People were just desperate to get them. It's like they knew it was going to be no short-lived power cut, that this one was serious and it could last days."
Most people were concerned about their fridges and freezers and losing hundreds of dollars' worth of food, he said.
When generators sold out they started selling people battery inverters, which operate through a car cigarette lighter. When they sold out, people started buying gas cookers and barbecues, Mr Mailman said.
The store had to buy 20 more generators, which were being delivered yesterday.
Mr Mailman said the Mitre 10 stores in Palmerston North and Hawera had also sold out of generators, camping gear and battery inverters.
Grant Harrison, owner of Harrisons Hiremaster in Wanganui, said their generators were all gone by 10am on Saturday.
"Everyone was trying to save freezers full of food. A lot of them said they were sharing the generator among four households, rotating it from one house to the another to keep the food chilled and frozen."
There was a waiting list of people wanting generators, he said.
Wanganui's supermarkets did a roaring trade in batteries, candles and matches.