They've long been illegal in Australia but last week's law change allows banks to raise funds from this market, limiting them to up to 8 per cent of the bank's assets. In New Zealand, the threshold is 10 per cent.
The National Australia Bank-owned BNZ has raised about $3.5 billion in covered bonds, representing about 6 per cent of its total assets, and will maintain a buffer between the bonds it has on issue and the Reserve Bank's 10 per cent limit.
"My guess will be that offshore would be the next best opportunity to do more covered bonds, probably Europe," said BNZ's head of debt capital markets, Mike Faville.
Covered bonds were a long-established asset class, used in Europe for centuries, and the bank saw them as a useful funding tool.
The covered bond market is booming, €120 billion issued globally in the first seven months of this year. In the past five years, issuers from more countries have used covered bonds to refinance mortgage lending.
Director Peter Sikora said Standard & Poor's was comfortable with local banks using this avenue of funding, because it allowed them to diversify and extend the maturity of their funding, and made them less susceptible to refinancing risk.