It needs to keep rates low to spur inflation - currently tracking at a 0.4 per cent annual rate - back to within a target range of 1 to 3 per cent, while also being mindful of the impact low interest rates are having on the heated housing market.
"I would say that we haven't seen the end of macro-prudential interventions [aimed at cooling property prices] by the Reserve Bank," McLean said.
The median house price in Auckland jumped to $820,000, past $800,000 for the first time, in March and was up 14 per cent from a year earlier, according to Real Estate Institute of New Zealand figures.
Westpac New Zealand grew its mortgage lending by 6 per cent, to $43.4 billion, in the six months to March.
The bank said it had been taking a "measured approach" to home loans.
Total net loans rose 8 per cent to $71.7 billion.
McLean said the bank had carried out stringent "stress testing" on its mortgage book.
"We're very comfortable with the shape of our portfolio and the quality of our book," he said. "Even under really adverse stress scenarios we can't get to scary numbers on the losses."