The bank's mortgage book grew by $792 million to $7.79 billion in the three months ended June 30, its latest general disclosure statement shows.

Using Reserve Bank figures as a proxy for all lending on mortgages by registered banks, that means Kiwibank accounted for a staggering 44.8% of the $1.77 billion of new lending in the quarter.

And yet, again using Reserve Bank figures, Kiwibank's market share at June 30 was just 4.9%, up from 4.45% at March 31 and 3.36% in June last year.

In the year ended June 30, Kiwibank's mortgage book grew by $2.69 billion, accounting for 38.1% of all mortgage lending by registered banks.

Not surprisingly, this explosive growth has had to be funded by additional capital. Kiwibank's parent, New Zealand Post, contributed a further $20 million in April and the bank also raised $60 million in "Tier ll" capital through a subordinated debt issue in September 2008.

Kiwibank's capital adequacy ratio was 10.5% at June 30, well above the Reserve Bank's minimum 8%.

While Kiwibank says it is now moving towards being self-funding, a bank spokesman says that doesn't necessarily rule out further capital injections if the bank's growth requires it.

Kiwibank's net profit in the three months ended June 30 rose to $12.4 million, up 83.4% from the same quarter a year earlier. That took annual net profit to $52.5 million, up 42.7% on the previous year. Both the latest quarterly and annual profit figures are before a one-off $11.1 million restructuring gain.

The profit figures are after a $4.6 million increase in charges against profit for impaired loans in the three months ended June 30, taking the annual impairment charges to $14.3 million compared with just $4.1 million in the previous year.

Of Kiwibank's $669.6 million of mortgages with loan-to-valuation ratios (LVRs) above 90%, $220.9 million were part of the government's Welcome Home scheme. Kiwibank also had $814.6 million of home loans with LVRs between 80% and 90% but says all loans with LVRs above 80% which aren't Welcome Home loans are covered by loan mortgage insurance.