Police filming in the streets could be in breach of privacy laws.

Frontline officers take cameras to disorder callouts, leaving them recording on the car dashboard or carrying them into the fray.

Police say it is a good way to gather evidence and see how crowds behave, as well as protecting officers from false complaints about their conduct.

But the Privacy Commission says police need to be careful that the practice is not breaching people's rights.

Canterbury police operations manager Inspector Craig McKay said his teams had used cameras successfully at riots and events such as Undie 500 rallies.

They had also taken cameras into bars they were investigating disorder or a host-responsibility breach, he said.

"Certainly all groups would benefit from having one. It's 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 filmed while drinking at a bar contacted The Press, objecting to the practice.

He said he filmed the officer with the camera on his cellphone, but his footage was erased after he was arrested for disorderly behaviour.

The bar owner, who did not want to be named, said the practice was "rude".

A Privacy Commission spokeswoman said police needed to ensure they were not breaching the Privacy Act. "They need to make people aware that they will be filming and let people know why.

"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.

"There could be instances when the police need to film covertly, so filming would be allowed without advising the public, though it would be very unusual for this to occur."

POLICE BEING EQUIPPED WITH LATEST TECHNOLOGY

West Coast police have embraced the digital age and Canterbury police may be next in line.

Frontline constables across the country are being armed with iPhones, Blackberrys, laptops and tablets as part of a pilot "mobility project" aimed at reducing crime at a lower cost.

It is the first widespread rollout of cellphones in the police, with 5000 phones to be deployed by this time next year.

Constables now use their own cellphones or share one from a pool. Only those ranked sergeant and above get a work cellphone.

The new phones will come with crime-fighting applications, including one that converts a photograph of a crime scene into a floor plan and another that helps with translating. More police-specific apps are being developed by their information technology section.

Police in Greymouth, Hokitika, Reefton and Westport have been trialling smartphones since January and received laptops and tablets on Tuesday.

Exact timeframes for a national rollout have yet to be determined, but Canterbury police are likely to get the phones early next year.

Project leader Inspector Simon Feltham said the technology had "huge potential".

- © Fairfax NZ News