Over the past 10 years, the average new first-home mortgage has increased from about $300,000 to more than $550,000, Reserve Bank data shows.

On a mortgage rate of 5.99 percent, that is $1520 a fortnight over 30 years, compared to $829 on 2014's numbers.

That increased debt means recent buyers are likely to be carrying much higher debt servicing costs into the future, even as home loan interest rates fall.

At the same time, the average household income has increased from just over $90,000 to about $130,000.

New loans to other owner-occupiers increased from less than $140,000 on average in 2014 to $310,740.

Data from the Finance and Mortgage Advisors Association of New Zealand estimates that 59 percent of New Zealanders are paying more than 30 percent of their household income in home loan costs.

Nearly a quarter spend more than half their income.

Of those under stress, 27 percent told the association's research they were mortgage prisoners because they could not refinance due to the servicing requirements of lenders or other financial circumstances.

Centrix data showed mortgage arrears rose slightly in September, with 21,200 home loans past due, marking a 13 percent year-on-year increase.

Infometrics chief forecaster Gareth Kiernan said a higher level of mortgage stress, or repayments as a percentage of income, was more common now. "But that doesn't mean we should necessarily accept it or normalise it.

Otherwise we run the risk of accepting that housing is permanently unaffordable in this country when, in reality, if anyone had been presented with the current house price versus income relativity 25 years ago, they would have said it was ridiculous and demanded that something be done to prevent that outcome occurring."

He said the way housing cycles worked meant unaffordable conditions were likely to persist for longer than instances of overly cheap housing.

"Because it is easier for house prices to rise rather than fall. So although we saw a reduction of 15 percent in house prices during 2022 and 2023, they are still substantially higher than they were pre-Covid.  Unless something significant occurs to drive house prices substantially lower again, the return of the house-price-to-income ratio towards a more acceptable level has to be primarily driven by higher incomes - which is a slow and drawn out process, particularly when the labour market is weakening and limiting income growth."

He said while the traditional benchmark of "affordability" of 30 percent of income on repayments might feel too low given how difficult it was for modern buyers to achieve that, it was a reasonable long-term target.

"And provides additional grounds for the government to try and make significant progress in improving the supply of land and housing and bringing down house prices, relative to incomes, over the medium term."

Kelvin Davidson, chief property economist at Corelogic, said housing affordability measures looked worse as house prices had risen in relation to incomes. Affordability had become more stretched over the past seven or eight years, he said.

"Mortgage servicing as a share of average income is higher than it used to be. From that sense it's definitely got harder but people keep finding a way."

But the share of purchases going to first-home buyers remains at record levels.

Davidson said people were helped by their more significant KiwiSaver balances and banks offering some low-deposit loans within the loan-to-value restrictions.

He said people who bought a house recently, particularly at the peak of the market, would face higher debt servicing costs for longer.

But most borrowers had much smaller loans and had been helped over time by their incomes increasing as the amount they owed reduced. fell.

-RNZ.