Seven floors of the under-demolition Copthorne Hotel in central Christchurch collapsed without warning on Saturday afternoon.
Police were called to the scene about 1.30pm to find seven storeys of the unoccupied building had pancaked, leaving two outer walls standing.
The collapsed Copthorne Hotel in Christchurch. Photo: RNZ
Police have had no reports of injuries, but they believe there was one workman on the site at the time.
The hotel is in the process of being demolished and it's not clear what caused the collapse.
Two outer walls have been left standing by themselves and debris is piled up on the ground in between them.
A Christchurch man who witnessed the collapse, Rob Henderson, says a digger operator was working on the the building before it pancaked.
Mr Henderson says he had to run away from the building to escape the dust created by the collapse.
He says he saw the digger operator and the site supervisor walking around the perimeter afterwards.
The area has been cordoned off in case more of the building falls.
Police have handed control of the site to the Canterbury Earthquake Recovery Authority.