Wellington City Mayor Justin Lester says there's a "reasonable likelihood" the central library will be demolished and rebuilt.
The Central Library was closed suddenly in March due to worries about its safety in a large earthquake.
The building was found to be at 15 percent of code, according to new standards, which means it is at risk of pancaking or collapsing in the event of the a major earthquake.
"I can't have that happening in our city," Mr Lester told Morning Report.
"While this is devastating - it's gutting for us to have to deal with this - it does present a wonderful opportunity to build a modern library that's focussed on the future," he said.
Meanwhile, in another blow to the "heart" of Wellington, the fern globe that hangs above the capital's Civic Square has been pulled down again for remedial work, less than a year after being returned after repairs.
Neil Dawson's fern sculpture was removed in 2015 for repairs and it took three years for it to return to the square.
Mr Lester said he could not speak out of turn about the dome, because the project was led by the sculptor's trust, however he said it should be back up within two months.
He said it was a matter of checking the wire connections.
"It is a windy location, we all know the Wellington wind can have an effect sometimes and the last thing you want is that it did come down.
"That's not expected, not anticipated but the best thing to do is to exercise caution."
The Town Hall, council offices and a children's creative centre are also closed for strengthening work. And there are concerns for the nearby City-to-Sea bridge.