For an average family using 8000kWh per year, the cost will be $800 more than last year.
Dr O'Sullivan said his work regularly took him into the homes of people hard hit by the economic downturn.
Many patients' homes were cold and damp but some wouldn't turn their heaters on because of the high cost of power.
Others switched off their hot water cylinders, or used LPG heaters which were cheaper to run but created a lot of moisture and worsened respiratory conditions.
Children in cold, damp homes were also at risk of chest and ear infections.
"A lot of high-needs people live in leaky, draughty homes. With the sale of state-owned energy companies, this is an example of how things are potentially going to get worse as power costs are dictated by commercial goals," he said.
New Zealand would pay long-term for unregulated power prices with higher hospital admissions and more people on welfare because they were too sick to work, Dr O'Sullivan said.
An inquiry was overdue into surging power prices in low socio-economic communities, which were "gouging the poor", said Tai Tokerau MP Hone Harawira.
"I know of families switching to candles which is a worry, oldies switching off their hot water because they can't afford hot water cylinders and kids being asked to stay in school and complete their homework because parents can't afford to keep their lights on at home."
Mr Harawira hoped to meet Far North Mayor Wayne Brown to discuss the price hikes, assess whether they were justified and see if there was anything they could do.
He also feared part-privatisation would be hard on the poor, who could be forced to choose between electricity and food.
The only positive for Northland was its milder weather than other parts of the country.
Mid North Age Concern manager June Duxfield wants a ceiling on power prices.
"A cap on the level the elderly and pensioners have to pay might be a way to go," she said.
Energy Minister Phil Heatley said the main reason for rising prices was the huge investment by Transpower and line companies into national and local grids.
"To slow price increases down, the Government introduced reforms in 2009 to improve choice for consumers, and opportunities are working well for those who give them a go," he said.
Northland MP Mike Sabin blamed power prices on the high proportion of domestic consumers compared to commercial and industrial users.
"The net result of this is that there are higher risks and lower returns for the electricity retailers, which is unfortunately reflected in their prices," he said.
Mr Sabin urged people to shop around and take advantage of the 'What's My Number' campaign.
Northland fire safety officer Craig Bain said people using candles should keep them away from combustibles and extinguish them before going to bed.
To see if you are paying too much for power, find a recent power bill and go to www.whatsmynumber.org.nz or www.powerswitch.co.nz. Type in your power usage and it will tell you how much other companies charge for the same amount of power. If you don't have a computer, the Citizens Advice Bureau can help.
