The unnamed bank could also occupy 14% of the second floor.
The iwi-based business group has lodged a land-use consent application to seal about 20sq m in front of the historic courthouse in the precinct, now known as Guilty Bar, and use the area as an outdoor seating and dining area within the permitted hours of 8am and 10pm.
Ngai Tahu Property Ltd development manager Gordon Craig, of Christchurch, said most of the pre-leasing was in place and the budget and timeline were being adhered to for the construction of Post Office Precinct One.
"POP One" was the final building being constructed in the five-building complex.
Mr Craig said POP One was on course for completion by September. Naylor Love Construction and sub-contractors were working on site.
"We've finished the basement and we're expecting to take sheet piling from the creek in early February. The ground floor is well under way [and work continues] on part of the structure for the upper floors."
The bank, New Zealand Post, Anderson Lloyd lawyers and WHK Cook Adam Ward Wilson accountants are expected to start moving into POP One in October.
The new three-storey building will have a basement car park with 32 bays.
NZ Post would move into half of the ground floor from its premises in POP Four.
The bank would occupy the other half and possibly some on the second floor, with up to 86% set aside for Anderson Lloyd.
The first floor would be taken up entirely by WHK Cook Adam Ward Wilson, which would merge its offices in POP Four and on Athol St under one roof.
A public piazza beside Horne Creek was planned to create a thoroughfare of outdoor seating, plantings and verandas between Camp, Ballarat and Stanley Sts.
Mr Craig said Ngai Tahu had received some expressions of interest for the cafe on the ground floor and the vacant areas in POP Four, but would be "going to the market" this month.
An existing, undisclosed Queenstown tenant was lined-up for part of POP Four's ground floor.
