Tauranga is now the most unaffordable city in New Zealand.

The annual Demographia International Housing Affordability Survey shows Tauranga residents must spend nearly nine years of full household income to buy a median-priced house.

Survey co-author Hugh Pavletich explained why the Bay of Plenty town's now more unaffordable than Auckland.

"Tauranga is very much a favoured retirement destination, so the household incomes will be much lower than Auckland's," he said.

Aucklanders need to spend 8.9 years of household income to buy a median-priced home, the survey shows.

Conversely, Christchurch and Dunedin are the most affordable markets in the country.