Several metres of a top tier of the three-tiered Oamaru stone wall near the intersection of Severn St and Douglas Tce failed about 4pm.
In March, the Waitaki District Council spent $45,000 improving the wall's stability, removing leaning sections, re-establishing drainage and building a new stone wall.
Waitaki Mayor Gary Kircher said part of the newly built section of the wall had collapsed, along with an older section.
While the exact cause of the collapse was unknown, he believed it could be due to several factors, such as heavy rain over the past few days and the weight of the soil and plant life behind the wall that had pushed it forward.
"There's definitely no answers at this stage.
"There's a number of options and a combination of things may have happened.''
He was not concerned about the quality of workmanship.
"As far as I know it's been rebuilt as it had been [previously] and that the work had been carried out well. If anything, there's better drainage.''
The original wall was built about 80 years ago by the Oamaru Beautifying Society from blocks of Oamaru stone, and the entire lower level was rebuilt about seven years ago using concrete and an Oamaru stone veneer.
That wall did not fail on Saturday. Council staff inspected the damage yesterday morning and said it was believed the wall did not pose a safety hazard at this stage.
Mr Kircher said the council would investigate its options once the exact cause of the collapse was known, which was expected to take several days.
"Our engineers will work on it.
"We will work out what the options are when the causes are known.
"I'm certainly keen to see it retained in its original form ... [but] that remains to be seen.''
No-one was injured as a result of the collapse and the highway remained open.
- Daniel Birchfield
