Northland households shelled out $11.5 million more for power than they needed to in the past year by not switching to the cheapest provider.
Figures from Consumer Powerswitch and the Electricity Authority show each household in the region on the most expensive plan overpaid for power by more than $400 in the year to October 2016.
The authority said the rate of switching power companies by Northland's residential power users during the one-year period was 16 per cent compared to the national average of 21 per cent.
If all the residential customers had switched to the cheapest provider, which was Nova, they would not have had to pay an additional $11.5m.
Whangarei mother Krystle Turdeich is one of those who has changed, switching three electricity suppliers in the last four months after moving to the district from Australia six months ago.
Initially, she was with Genesis and said her power bill was $689 a month so she switched to Contact and saved about $100.
"I am on the verge of having a bad credit record because I can't afford to keep paying high bills for power," the sales' consultant said.
Ms Turdeich is now with Powershop, the same company she had in Melbourne, and she is waiting for her first bill. She said power prices in Australia were about one-sixth of that in New Zealand.
"Something needs to be done about the high power prices here because it's not fair on people.
"Even on those who are employed, because they get paid $15 to $19 an hour, and they struggle with the cost of electricity," she said.
There were 87,983 residential customers in Northland in the year to October 2016 and Genesis had the most customers with 12,912 and Electric Kiwi the least at 33.
Nova was the cheapest provider with an average household paying $2014 annually while Mercury was the most expensive, charging $2425.
In Whangarei and Kaipara, 9178 of the 56,620 households switched electricity providers during the one-year period while the number in the Far North district was 5111 out of 31,363 homes.
In the past year, Northlanders overpaid for power by more than $11m and New Zealand households by more than $300m.
Northland has some of the highest power prices in the country because of its distance from conventional power sources.
Meanwhile, a new electricity provider in Northland, which claims to be the cheapest, has challenged other small retailers to follow its lead and bring greater price competition in the region.
Powershop said its average annual price per household would be $2033.
"The region is dominated by large industry players which are typically more expensive than newer and smaller retailers. Households haven't had a lot of choice which is why switching rates are so low," Powershop's Mark Soper said.