Hartzer said the institutional bank's performance was hurt by an A$85 million tax charge.
The New Zealand unit widened its net interest margin to 2.29 per cent in the period from 2.28 per cent a year earlier, as cheaper wholesale funding costs and improved deposit spreads offset competitive pressure in the mortgage market.
About half of the New Zealand unit's growth in business lending was in agriculture, which has been a major focus for the bank in recent years. The food processing sector had also helped boost commercial lending for the bank in the half, it said.
Westpac's New Zealand term deposits grew 2 per cent to $25.1 billion from a year earlier, while other deposits grew 10 per cent to $26.4 billion.
Non-interest income rose 3 per cent to $245 million as funds under management swelled 22 per cent to $6 billion.
The parent's board declared an interim dividend of 93 Australian cents per share, unchanged from a year earlier, with a May 15 record date.
The dual-listed shares were unchanged at $38.32 on the NZX and have gained 11 per cent this year.