LONDON (AP) — London police will start using facial recognition cameras to pick out suspects from street crowds in real time, in a major advance for the controversial technology that raises worries about automated surveillance and erosion of privacy rights.

The Metropolitan Police Service said Friday that after a series of trials, the cameras will be put to work within a month in operational deployments of around 5-6 hours at potential crime hotspots. The locations would be chosen based on intelligence but the police did not say where, the number of places, or how many cameras would be deployed.

Real-time crowd surveillance by British police is among the more aggressive uses of facial recognition in wealthy democracies and raises questions about how the technology will enter people’s daily lives. Authorities and private companies are eager to use facial recognition but rights groups say it threatens civil liberties and represents an expansion of surveillance.

London’s decision to use the technology defies warnings from rights groups, lawmakers and independent experts, Amnesty International researcher Anna Bacciarelli said.

“Facial recognition technology poses a huge threat to human rights, including the rights to privacy, non-discrimination, freedom of expression, association and peaceful assembly,” Bacciarelli said.

London police said the facial recognition system, which runs on technology from Japan’s NEC, looks for faces in crowds to see if they match any on “watchlists” of up to 2,500 people wanted for serious and violent offences, including gun and knife crimes and child sexual exploitation.

“As a modern police force, I believe that we have a duty to use new technologies to keep people safe in London,” Assistant Commissioner Nick Ephgrave said in a statement.

The British have long become accustomed to video surveillance, with cameras used in public spaces for decades by security forces fighting terror threats. Real-time monitoring will put that tolerance to the test.

London is the sixth most monitored city in the world, with nearly 628,000 surveillance cameras, according to a report by Comparitech.

London’s move comes after a British High Court ruling last year cleared a similar deployment by South Wales police, which has been using it since 2017 to monitor big events like soccer games, royal visits and airshows.