Westpac New Zealand said it had an offer of September 2018 bonds aimed at raising up to $800 million.
The offer, which closes on Friday, follows last year's successful five-year bond issue, which had to be expanded to meet investor demand.
Westpac treasurer Jim Reardon said the issue would "re-tap" last year's issue and would be mutually interchangeable with it.
The latest addition to the bank's bond offering would give investors a deeper liquidity pool to trade bonds.
Reardon said that despite uncertainty in world markets, the current environment offered a "relatively clean" window of opportunity for the bank to raise funds.