A pane of glass has fallen 12 storeys on Auckland's busy Wyndham St, raining glass while many office workers took their lunch break
The broken window was about 1 metre by 1.5 and is the third to fall in a year at AMI House.
Property manager Bob Rogers said the reason for this was unknown but he would be looking into it.
"Since it happened last time, we've had the windows looked at," Mr Rogers said.
He said no issues were apparent after the inspection.
"We have the windows cleaned on a regular basis and the cleaners advise us if there are any problems but it's a bit of a mystery," Mr Rogers said.
He said the previous breaks happened in the summer when the weather was hot and it was thought that that could have been a cause but he said that is unlikely to be the cause today.
A policewoman at the scene, who declined to give her name, said no one was injured.
"We're very lucky," she said.
Senior station officer Barry Fox said firefighters had no idea how the window was broken.
"There was no human involvement, maybe it was some sort of movement," Mr Fox said.
Some passers by ignored the cordon and walked underneath the building with their bags over their heads.
No one was injured in the accident.