Extensive remedial work and expert construction advice are needed, the Dunedin City Council has said.
Property services group manager Dave Bainbridge-Zafar said the cost and timeframe would not be known until investigation and design work had been completed, but repairs would involve specialist work and would likely take several years to complete.
The council hoped to have work under way by mid-2021.
A problem became apparent in November last year after a piece of ornamental Oamaru stone fell from the Municipal Chambers.
Scaffolding and netting were assembled as a precaution around the chambers and hall, because both were due for remedial work.
The public building complex is one of Dunedin’s most prominent and the city council has slated repairing and preserving its integrity, weather-tightness and character as a priority.
The council has requested proposals from contractors that would be able to provide technical advice, help in the design process and manage the physical work.
Submissions close next Tuesday.
Mr Bainbridge-Zafar said the Municipal Chambers in the Octagon was one of Dunedin's oldest buildings and required specialist input and advice to ensure issues were fully understood.
The Municipal Chambers opened in 1880.
The town hall, behind the chambers, was built in 1929.
Mr Bainbridge-Zafar said the council was assessing the level and scope of work needed.
"We will be in a position to give more details once this work is complete."
Nobody was hurt when the stone fell from the chambers building.
