Police have developed a specialist software tool which mines social media for information.
The Signal tool was developed for high-profile public events and emergencies and works by scanning public-facing material on social media networks such as Facebook and Twitter.
Police director of intelligence Mark Evans said it was "not typically" used as an evidence gathering or investigative tool although it could be.
Social media use by law enforcement around the world has grown with the International Association of Police Chiefs finding 77 per cent of agencies used it most commonly to investigate crime. The survey of 600 agencies across the United States found it had helped solve crimes.
Mr Evans said the tool was developed as part of preparations for the Rugby World Cup because police "wanted the ability to scan social media comments in and around the stadiums in real time".
Since then, it had been used for royal visits, Waitangi Day and during the Auckland cyclone.
Mr Evans said Signal was not used to crawl random postings. Instead, police would set a geographical area and put in key words.
As an example, he said a large sporting event could see "protest", "traffic", "accident" or "delays".
He said the strength of Signal was its ability to help police "identify and analyse social media feeds relevant to crime and public safety" at a specific time and place.
In doing so, Mr Evans said police were able to judge the impact of an event which had happened or stop a problem escalating. It also helped target people and resources where they were needed, he said.
During the Rugby World Cup, it allowed police to detect a boy racer convoy heading from Auckland to Hamilton.
The drivers "felt they would be able to get away with dangerous behaviour on the roads because they believed police resources would be busy elsewhere", he said.
Other uses during the cup alerted police to a flash mob haka planned for one competing team and a protest targeting another team passing through Auckland International Airport. "Social media occurring in the public domain is just another public space and police need a presence in that space in the same way we need to be seen in neighbourhoods and on the roads."
Mr Evans said Signal's use was limited to police intelligence staff and other authorised officers. He said it could be used for crime investigation but its use was limited because it only scanned public posts.
Signal was developed as part of a $60,000 emergency management tool.
Global police use of social media
53 per cent - Created a fake profile or undercover identity
48 per cent - Posted surveillance video or images
86 per cent - Viewed profiles of suspects
49 per cent - Viewed profiles of victims
Source: IACP Social Media Survey 2012