The South Island has had bigger median income gains than the North over the past seven years, Census figures show.
But an expert cautions that the figures may point to changing work and migration patterns, rather than real growth in income for the same people.
Statistics New Zealand figures drawn from last year's Census show all regions in the South Island, except for the Queenstown-Lakes District, have had growth in real median income.
Buller District's median income increase was up 19 per cent on 2006. Ashburton and Southland District had increases of 14 and 11.7 per cent.
In the North Island, New Plymouth and Stratford District had the largest increases with 8.5 and 7.4 per cent.
Median incomes in Auckland, the central North Island and some East Coast regions were down on the 2006 Census.
Other North Island regions had modest growth in the range of less than 1 to 3 per cent.
University of Canterbury economist Eric Crampton said differences in income for men aged between 30 and 55 were related to differing labour market conditions.
"If some regions had, for example, stagnating personal income but increases in income among those in that age group, we might look to demographic changes, like more retirees on lower incomes or changing labour force participation among second-earners, to explain regional differences.
"If you instead had stagnant income among working-aged males, then that could point to bigger problems in unemployment, regional productivity or hits to regional industry."
Dr Crampton said people on low incomes because of unemployment in rural regions might move to the city to seek work.
"If those unemployed in the regions were more likely to move to the big city while those unemployed in the city were less likely to leave, that, too, could explain some of the difference in regional income growth.
"We would also want to look closely at international migration patterns. Auckland draws a lot of New Zealand's recent migrants. Dropping real income in Auckland among those who have been there a long time would be very different to a decrease in median real income driven by a lot of inbound migration of lower-income people."
AUT sociology professor Charles Crothers said the Census statistics undervalued the economic activity for self-employed people.
"Particularly for farmers - they have rather more economic power than indicated by their reported income," he said.
"I do think people are a bit wary of the Inland Revenue Department, even when it comes to the Census.
It's also hard for some people to work out their income."
Statistics NZ said the Census question on income had a high non-response rate, with 9.7 per cent of respondents refusing to say how much they made.
Recruitment expert Samantha Gadd, founder of the HR Shop, gives her tips on how to get a pay rise in 2014.
1. Show your employer what they are going to get for their money: Be clear on what the expectations are in your role and work to exceed them. You have got to be doing more than you're expected to do, so that entails taking on additional projects, taking on a more senior role or any recent achievements.
2. Pick your time: It is a good idea to wait until your annual review and discuss it in person, ideally, one on one with your employer somewhere private.
3. Don't aim too high: You don't want to make your employee think you are greedy by using the tactic of asking for more than you should reasonably expect.
4. Do your homework: Talk to colleagues from other firms and look at online salary surveys to establish average wages in your industry.
5. If you are turned down: Look at the reasons - was it your individual performance or market conditions? If there is no money for raises, could you negotiate extra annual leave, some professional development or other perks?