Lender Firstmac has warned mortgage brokers about plans to toughen lending criteria to high-density apartments, further scaring the real estate market regarding a property bubble.

"It is quite obvious there is going to be a problem in the future," said Kim Cannon, FirstMac chief executive, regarding the reason why they are tightening their lending criteria. "Look at the number of cranes everywhere. In the cities, along train lines in the outer suburbs, there are apartments being built and people are beginning to ask who is going to live in them."

Firstmac's crackdown targets both non-residents and investors, although Cannon added that they are focusing only on high-quality low-rise dwellings.

As a non-bank lender, Firstmac generates funding from overseas investors. This forces them to be conservative about lending as there is a risk that overseas buyers who purchased multiple apartments because of generous conditions offered by banks could forfeit deposits and renege on off-the-plan purchases.

According to Firstmac's new arrangements, any apartment in a development with more than six floors is already considered "high-density." This will hit large numbers of high-rise apartments in Brisbane—the lender's hometown—its central business district, inner suburbs, and the Gold Coast. This will also have an impact around central Sydney and Melbourne and surrounding high-rise precincts.

Loans over 70 per cent and up to 80 per cent will be considered if the borrowers have lender's mortgage insurance. Loans of up to 70 per cent of the apartment's value can be considered but rental income will not be included for servicing the debt.

Other lenders, such as Macquarie Bank, AMP Bank, and Teachers Mutual Bank, have also tightened their policies on apartment lending.