Auckland Council building inspectors have been investigating after a ceiling partially collapsed in the Event Cinemas complex in Newmarket.
A preliminary report says a decades-old strap holding an air conditioning duct wore away, dropping the duct and pipes through the ceiling panels.
Few people were about at the time, with a scratched arm the only reported injury.
Acting building control manager for Auckland Council Tim Weight says the strap had been in place for 25 years.
Mr Weight says the matter will now be raised with independently accredited building inspectors for commercial buildings.
Worksafe New Zealand says it won't be investigating as no serious harm was caused and it's a council matter.
Fire and ambulance services were called shortly before 10am on Tuesday to the cinema after the air conditioning pipes fell through the ceiling.
Radio New Zealand's reporter at the scene said the collapse was on the first floor foyer of the theatre, and an area of ceiling about 5 metres by 5 metres had fallen onto the customer lounge area.
The Fire Service sent specialist rescue tenders and an aerial appliance to the building but these had since been stood down. It described the roof collapse as minor.
Staff isolated the unstable area and engineers carried out a safety check before disconnecting some of the air conditioning pipes.
Event Cinemas manager Carmen Switzer says the pipe at fault was old and not in use, and it was not yet known why it fell through the ceiling.
The cinema had just been refurbished and gone through council compliance checks, she said.
The complex remained open while the debris was being cleaned up.