Figures released by property valuation website myvalocity for September show the number of new residential mortgage registrations declined by 21 per cent.
Auckland saw the largest reduction in the number of new mortgage registrations, down 26.2 per cent on the same time last year.
The North Island's metro centres were also down 15.6 per cent compared to September 2015.
Wellington and the South Island metro centres buck the downward trend with growth in the number of mortgages of 2.8 per cent on the same time last year.
Myvalocity chief executive Carmen Vicelich said the figures reinforced the view the property market was cooling.
"Mortgage registrations are a good indicator of the financial performance of the market as it tracks the behaviour of all active buyers rather than just what is actually selling at the time," Vicelich said in a statement.