Bells that weigh up to 12 tonnes inside the Carillon tower at the National War Memorial in Wellington are at risk of falling on people.
The Ministry for Culture and Heritage has released a detailed seismic assessment that it says shows this could happen in an earthquake.
"If an element of the bell-frames failed, there is a risk that one of the bells, or other material, could fall into the foyer of the Carillon Tower which is the main entry to the National War Memorial," it said in a statement.
"This could pose a significant risk to anyone in the foyer at the time."
The ministry was first warned the bells could fall down, by the same engineering firm, Dunning Thornton, in 2011.
It is now making "alternative arrangements" for national commemorations to be held within the wider Pukeahu National War Memorial Park while strengthening work goes on.
The ministry had part of the steel bell frame replaced during years of upgrade works from 2012-18 - but not all of it.
This included two years spent pulling apart the 15,000-part bell instrument, refurbishment, replacing badly corroded head bolts, then reinstalling the entire assembly.
But the ministry had knowingly failed to replace some of the bell-frame angle braces.
Now, the bell frame has been rated at just 15 percent of standard.
The engineers said in 2011 the ministry should get a detailed assessment done of the frame; it did not begin this till August 2019.
There was nothing to say there was any risk to anyone immediately outside the 50-metre-high tower, the ministry said today.
However, the seismic assessment completed in April, also shows the lower part of the bell tower is earthquake-prone at 25-30 percent of New Building Standard..
RNZ previously reported this after questioning the ministry about a summary of the seismic assessment it released earlier under the Official Information Act.
The tower has been closed since February, and with it the Hall of Memories - which is 100 percent NBS - but the Pukeahu park remains open.
The ministry now has less than two years to fully and finally strengthen the whole building.
"Our focus now is on making the necessary plans to get the National War Memorial strengthened and open again, so it can continue to be the place of solace, remembrance and reflection it has been to generations of New Zealanders," the ministry said.