– London's police department said Friday that it would begin using facial recognition to spot criminal suspects, using video cameras as they walk the streets, adopting a level of surveillance that is rare outside China.

The decision is a major development in the use of a technology that has set off a worldwide debate about the balance between security and privacy. Police departments contend that the software gives them a way to catch criminals who may otherwise avoid detection. Critics say the technology is an invasion of privacy, has spotty accuracy and is being introduced without adequate public discussion.

Britain has been at the forefront of the debate. In a country with a history of terrorist attacks, police surveillance has traditionally been more accepted than in other Western countries. Closed circuit television cameras line the streets.

The technology London plans to deploy goes beyond many of the facial recognition systems used elsewhere, which match a photo against a database to identify a person. The new tools use software that can immediately identify people on a police watch list as soon as they are filmed on a video camera.

The Metropolitan Police said in a statement that the technology would help quickly identify and apprehend suspects and help "tackle serious crime, including serious violence, gun and knife crime, child sexual exploitation and help protect the vulnerable."

In November, the police shot and killed a man wearing a fake bomb on London Bridge after two people were fatally stabbed. The police called the attack a terror incident.

"Every day, our police officers are briefed about suspects they should look out for," Nick Ephgrave, assistant commissioner of the police department, said in the statement. Live facial recognition, he said, "improves the effectiveness of this tactic."

Facial recognition, already widespread in China, is gaining traction in Western countries. Many cities and police departments, like the New York City Police Department, use technology comparing photos and other static images against a database of mug shots.

Use of real-time facial recognition is less common. NEC, a Japanese company that makes biometric and facial recognition services, sold London the technology now being adopted. Other buyers include Surat, a city of about 5 million people in India, and the country of Georgia, according to the company's website.

Privacy groups criticized London's decision and vowed to take legal action to try to stop the deployment of the software.