The latest general disclosure statement for the Australian bank's New Zealand subsidiary shows net profit for the three months ended June was just $26 million compared with $163 million in the June quarter last year. That brought net profit for the nine months ended June to $186 million compared with $462 million in the same nine months a year earlier.

The quarterly profit fall largely reflected a further $199 million in charges against profit for bad loans, bringing the total for the nine months ended June to $515 million compared with just $97 million in the same nine months a year earlier.

Net interest income fell 9.3% to $321 million in the June quarter but was up 7% at $1.02 billion for the nine months ended June.

Most of Westpac's burgeoning bad debts are from its corporate lending - mortgages gone bad accounted for just $20 million of the June quarter charges and $70 million for the nine months ended June.

Westpac's mortgage book totalled $27.02 billion at June 30, up $136 million from March 31. Using Reserve Bank figures as a proxy for the market, Westpac's new mortgage lending accounted for only 7.7% of the increase in lending on mortgages by registered banks in the June quarter.

That meant its market share slipped from 17.09% to just below 17%.

Its mortgage lending in the March quarter grew $365 million after adding just $60 million in the December quarter.

Westpac had a further $5.18 billion in undrawn mortgages at June 30.

Westpac's mortgages with loan-to-value ratios (LVRs) above 80% continued to decline to 26.9% of its mortgage book at June 30 from 27.4% at March 31 and 28.2% at December 31.