Police said the system was designed to target "invisible crimes", such as driving an unlicensed vehicle or driving without insurance or while disqualified.

Patrick Pang Shu-hung, senior superintendent at the police traffic management and prosecutions bureau, said such offenders are not easily caught.

"An officer will not stop a car unless it is obviously violating traffic rules, such as by speeding or driving in a dangerous manner," he said.

"With this system, the efficiency and effectiveness of prosecutions could be enhanced. It could also reduce the number of problematic drivers on the road."

Cameras and computers will be installed on footbridges and at roadsides. Each camera covers one lane. Pang said that on stopping a vehicle, an officer will check that the driver is actually the offender in question.

He did not reveal how much the system cost, the duration of the trial period, or when exactly it would be launched.

Pang said the system would only be used to prosecute people for traffic violations, and that the information would be deleted from the system after each operation.

Labour Party lawmaker Cyd Ho Sau-lan, of the Legislative Council's security panel, said the system was unnecessary.

"If a driver did not pay his fines or if he did not have third-party insurance, the police should already have his information, and can make arrests via other means," she said.

"The police are using investigations as an excuse to invade privacy."

But the Automobile Association's James Kong Yat-hung said Hongkongers should not worry too much: "Compared to many other cameras in the city, these extra ones are nothing."