"However, we are going to turn this into a positive. It gives us the chance to rethink the plans for our central city and there is money already in the budget to make it the cultural heart of our district.
"Whatever we do now will carry us forward for at least the next 100 years. The age of the opera house is now."
The engineering reports confirmed that the masonry walls in the opera house that are not reinforced would be unsafe in an earthquake.
Both the opera house and adjoining municipal building were closed to the public last year.
Councillors have indicated that they want to make decisions on the project before Christmas.
A "pre-engagement" period asking for residents' feedback on the broad options is anticipated to start in September.
An independent working group has been set up and a project manager hired.
An engineer with 36 years' experience in New Zealand and overseas, Richard Kirby, will oversee the project and head an independent working party (IWP).
He will be joined by Peter Snelling, Chris O'Reilly, Genevieve Beech, Ngahiwi Tomoana, Gary McCalmont, Andy Coltart and Jenni Giblin.
"The aim of the IWP is to provide specialist, independent expert advice to the project and peer review the process so we can bring the very best possible options to the public," Mr Kirby said.