Both the Bankers Association and the Real Estate Institute say more people are going to second and third tier lenders to get money for home loan deposits.
Under new Reserve Bank rules, no more than 10% of a bank's mortgage lending can made be to customers with deposits of less than 20% from 1 October.
The Real Estate Institute says some real estate agents have reported they are helping prospective buyers access loans from non-bank lenders to get extra money for deposits.
The Bankers Association says that mirrors what has happened in other countries, like Sweden and Canada, which have limits on mortgage lending to people with low deposits.
The association says the Reserve Bank has signalled it may step in to regulate second and third tier lenders if needed.
New rules on low deposits now in effect
New rules for people wanting to get a housing mortgage with a low deposit come into effect on 1 October. Banks cannot now lend more than 10% to people with deposits of less than 20%.
The Reserve Bank argues low deposit loans will help protect the financial system from the shock of a collapse in the housing market. They will also delay the need to raise interest rates when inflation is low and the dollar is high.
The Government says it pushed for first-home buyers to be exempted, but the Reserve Bank argued that would have reduced the effectiveness of the new rules, as 30% - 40% of those affected are first-home buyers.
The Reserve Bank also decided not to exempt regions where houses are more affordable.
Changes to Kiwisaver and Welcome Home Loans, that the Government says will make it easier for people to buy their first home, also come into effect on 1 October.