As well, BNZ's normalised June quarter profit near doubled, reflecting changes in the fair value of financial instruments, although net interest income fell slightly, its latest general disclosure statement (GDS) shows.

The bank's mortgage book grew by $245 million to $26.01 billion in the three months. That compares with its $126 million growth in the March quarter, $129 million in the December quarter 2009, $196 million in the September 2009 quarter and $637 million in the June 2009 quarter.

Using Reserve Bank figures as a proxy for the market, BNZ increased its market share of mortgages written by registered banks to 15.81% at June 30 from $15.7% three months earlier.

Those central bank figures showed mortgage lending by registered banks slowed to $889 million in the June quarter from $1.47 billion in the March quarter.

BNZ's GDS shows the percentage of its mortgage book with loan-to-value ratios (LVRs) above 80% rose slightly to 10.6% at June 30 from 10.5% three months earlier. However, this is low compared to other banks - Westpac's mortgages with LVRs above 80% accounted for 23.6% of its book at June 30 while Kiwibanks accounted for 20.3%.

BNZ's normalised net profit, excluding tax charges and credits on its structured finance transactions, rose to $161 million in the three months ended June compared with $78 million in the same quarter last year, mainly because it recorded a $56 million net gain in fair value of financial instruments compared with an $81 million net loss in the same quarter last year.

Its nine-month normalised net profit was down 14.4% to $409 million - the $578 million bottom line profit included $167 million in tax credits relating to its structured finance transactions while the year-earlier nine-month $183 million bottom line loss included a $416 million tax charge relating to its structured finance transactions.

The bank's net interest income fell 1.8% to $325 million in the June quarter and was down 8.5% to $947 million for the nine months.