Massey University banking expert David Tripe said targeting investors was likely to be straightforward. He suggested that they could be identified by any rental income they were making on properties. But he said limiting the restrictions to Auckland - as Mr Little wanted - would be more difficult.
Associate Professor Tripe said investors would eventually get around any restrictions by shuffling their properties into family trusts or other ownership structures.
Mortgage specialist Bruce Patten, of LoanMarket, said extending lending restrictions to investors appeared to be a "natural progression" from the loan-to-value ratios imposed by the Reserve Bank in 2013. But he said any potential measures would take at least a year to introduce because banks did not have up-to-date information on whether their customers were owner-occupiers or investors.
Victoria University's chair in public finance Norman Gemmell said the policy was good in principle, but could be difficult in practice.
In a consultation paper last month, the Reserve Bank suggested that investors could be identified by the number of houses they owned or by the amount of rental income they were earning from a property.
Q&A: Bank moves
What is being proposed?
The Reserve Bank is considering making it harder for residential property investors to get a loan.
Why?
House sales to investors are increasing in Auckland, and they are believed to be contributing to higher house prices.
Do the proposals have support?
The Government says it would not veto moves by the Reserve Bank to curb lending to investors. Labour wants a crackdown on speculators, but only in Auckland.