Christchurch police filming incidents they attend could be breaching privacy laws, the Privacy Commission warns.
Officers called to disorder incidents take cameras to help gather evidence and avoid false complaints about police conduct.
But a Privacy Commission spokeswoman told The Press police needed to make people aware they were filming, and why, and ensure no one's rights were breached.
"They should also have clear policies about things like storage of the information and who will be able to get access to it," she said.
She said while there would be instances where police would need to film covertly without informing the public, such instances would be "very unusual".
Canterbury police operations manager Inspector Craig McKay said the footage captured by officers at riots and events like the Undie 500 car rally were "the best evidence we can use in court".
"This is no different from people holding up their iPhone or cellphone and filming the police deployment," he said.
A man arrested for disorderly behaviour complained to The Press that he had been filmed while drinking in a bar.
The bar's owner also objected to the practice, calling it "rude".