A spate of vandalism of the clocktower in The Square was pre-meditated says council.
Parks and Reserves manager, Kathy Dever-Tod says it is extremely disappointing that people would vandalise one of the city's landmarks.
"The Square does not contain rocks, which leads us to believe this was pre-meditated vandalism.
"For them to do it repeatedly is extremely disheartening."
"We expect our residents will be as frustrated and disappointed as we are, that people vandalised such an important site in our city.
She says the police are investigating and is urging anyone who knows anything to contact them.
On three separate occasions over the past month, the glass bricks surrounding the bottom of the clocktower have been smashed with rocks.
On one night alone more than 100 bricks were smashed.
Dever-Tod says the vandalism means the walls where the glass bricks were, need to be replaced.
The glass bricks were installed when The Square was upgraded in the early 2000s.
Council had a supply of spare bricks to replace ones that were broken accidentally, but there is not enough to replace the significant number of damaged ones.
The glass bricks were made overseas and are not currently in production.
Dever-Tod says even if enough glass bricks were available for replacement, the council would not be able to continue using glass bricks.
The structural system which holds the glass bricks in place has been degraded over time, to the point where reinstalling glass bricks is no longer an option.
She says the bricks are being replaced with a solution that will limit vandalism.
"The glass bricks are being removed and replaced with sheets of 12mm toughened glass with a 5mm toughened clear Perspex front as a protective layer.
"This new solution will not affect the quality of the evening lights."
The walls will have security fencing around them until the work is completed in a couple of months.