Westpac New Zealand's mortgage book grew by $477 million in the three months to December but its lending to people with less than a 20 percent deposit shrank by $105 million.
The bank's mortgage lending to those with more than a 20 percent deposit rose by $582 million in the quarter.
The Reserve Bank has ruled that from October last year, no bank can lend more than 10 percent of total new lending to people with less than a 20 percent deposit.
Westpac's December quarter profit jumped 55 percent to $247 million.
That reflected a near 5 percent rise in net interest income, a 55 percent jump in non-interest income, such as fees, and a slump in charges against profit for bad loans.