Auckland has the nation's highest rate of homeowners still paying off their mortgages and the lowest proportion who own their home mortgage-free.
Tasman homeowners, by contrast, are the most likely to have paid off their home while Gisborne has the highest proportion of renters.
The figures are from 2013 Census data released to the Herald by the Commission for Financial Literacy and Retirement Income.
They map the country's most mortgage-free regions and areas where you are least likely to own your own home.
Experts say the figures -- which also show Auckland has the second-highest rate of people living in rental accommodation -- are further evidence of soaring house prices across the city, which have trebled in some areas since 2000.
It means many homeowners who have over-extended themselves to buy property risk reaching retirement age still carrying tens of thousands of dollars in mortgage debt.
"There's a big percentage of people in Auckland who are unable to pay off their mortgages," said mortgage adviser for Loan Market, Bruce Patten.
"When they get to the point that they want to retire they're basically selling up and moving out of Auckland."
The figures show Auckland and Southland have the highest proportion of households who own their own home but are still making repayments (36 per cent).
But Auckland has the lowest percentage of households who own their homes outright (25 per cent), while Tasman homeowners are the most likely to be mortgage-free (40 per cent).
In terms of renters, Gisborne has the biggest proportion of people who don't own their own home (42 per cent) while Auckland has the second-highest figure for renters (39 per cent).
Mr Patten said the average purchase age for a first-home buyer had risen to 36, as people were forced to save bigger deposits to get on the property ladder.
"It means that some of them are going to struggle to pay their debt off by the time they retire."
Some Auckland homeowners who weren't able to be mortgage-free by retirement age were selling up and buying cheaper property in Tauranga, Napier or Marlborough.
"They have no choice. They either downgrade in Auckland or they downgrade out of Auckland to get rid of their debt."
Soaring house prices came on the back of immigration pressures and a shortage of available properties, forcing buyers to take out huge mortgages.
Real Estate Institute of New Zealand chief executive Helen O'Sullivan agreed Auckland's low rate of outright home ownership reflected price growth. The region's median sales price hit $615,000 last month -- a 7.9 per cent increase since September 2013.
"It takes longer to pay off a house in Auckland," Mrs O'Sullivan said. "But it's only been the last two years that we've seen Auckland's price growth outstrip the rest of the country."
The figures also reflected the number of domestic and immigrants moving to the city, who were more likely to rent until they decided where to settle down.
"The longer you've lived somewhere the more likely you are to have paid it off.
"Because Auckland's grown so much over the last 10 to 15 years so many of us are still only on the beginning of the [home ownership] pathway."
Sorted spokesman Tom Hartmann said carrying mortgage debt into retirement or long-term renting had ramifications for people's eventual financial security.
"New Zealand Super is built around the idea that people will own their own home freehold by the time they reach retirement."
Raewyn Fox, chief executive of the Federation of Family Budgeting Services, said home ownership was increasingly out of reach for many Kiwi families, which meant many would be paying rent in their retirement.
"We all grew up expecting by [retirement] we'll own our home and have somewhere to live but it's rapidly disappearing from people's horizons."
By Lane Nichols of the NZ Herald
