A monument in Pakaitore-Moutoa Gardens is so badly degraded it will cost up to $100,000 to fix, and will this week be fenced off for safety reasons.
A engineer's report commissioned by the Pakaitore Historic Reserve Board has found the World War I memorial is at potentially serious risk from both earthquakes and very strong winds.
The board's deputy chairman, Wanganui District councillor Hamish McDouall, said the monument, built in the 1920s, was not engineered "to the degree we expect today".
The monument consists of a base and obelisk with a marble statue of a soldier on top.
Mr McDouall said: "Over the years, the casing has cracked and the fill is being washed and blown out.
"The top 1m is actually hollow, so we have this beautiful marble statue standing on what is probably quite a fragile platform."
Mr McDouall said it was difficult to get a completely accurate picture of the state of the monument because it was so fragile.
He said fencing it off was an interim measure only until further work could be done.
Mr McDouall said the cost of repairs would be "tens of thousands of dollars", possibly up to $100,000. However, there were sources of funding available for the upgrade of war memorials.
Mr McDouall said the board had been planning the monument's overhaul for a couple of years, and hoped to have it completed before the 100th anniversary of the battle of Gallipoli in 2015. "We can't sit on our hands and do nothing," he said.