But rising fears of terrorism have lessened public hostility to surveillance cameras in the West. This has been particularly true in Britain, where the police already install the cameras widely on lamp poles and in subway stations and are developing face recognition software as well.

New York police announced last month that they would install more than 100 security cameras to monitor license plates in Lower Manhattan by the end of the year. Police officials also said they hoped to obtain financing to establish links to 3,000 public and private cameras in the area by the end of next year; no decision has been made on whether face recognition technology has become reliable enough to use without the risk of false arrests.

Shenzhen already has 180,000 indoor and outdoor closed-circuit television cameras owned by businesses and government agencies, and the police will have the right to link them on request into the same system as the 20,000 police cameras, according to China Public Security.

Some civil rights activists contend that the cameras in China and Britain are a violation of the right of privacy contained in the International Covenant on Civil and Political Rights.

Large-scale surveillance in China is more threatening than surveillance in Britain, they said when told of Shenzhen’s plans.

“I don’t think they are remotely comparable, and even in Britain it’s quite controversial,” said Dinah PoKempner, the general counsel of Human Rights Watch in New York. China has fewer limits on police power, fewer restrictions on how government agencies use the information they gather and fewer legal protections for those suspected of crime, she noted.

While most countries issue identity cards, and many gather a lot of information about citizens, China also appears poised to go much further in putting personal information on identity cards, Ms. PoKempner added.