SYDNEY will be scanned by sky-high spy cameras to catch arsonists in the act in a world first surveillance operation.

As new statistics reveal that a juvenile is now being charged, cautioned or sent for youth conferencing every five days for lighting fires, The Daily Telegraph can reveal that a network of new generation spy cameras is being planned for Sydney to catch them in the act.

A trial has been underway in Sydney's northern suburbs for the past week using the new technology to detect fires within minutes of being lit.

The first sentinel Firecam has been secured atop a tower in Hornsby. It has been automatically scanning the horizon for plumes of smoke at a radius of about 11km using recognition software which enables it to virtually think for itself.

Unsuspecting firebugs would be unaware it is programmed to lock on to a fire, zoom in and capture felons on film as they flee.

By then, it has also sent a self-generated alarm to fire headquarters to deploy authorities to the location.

The technology, adapted from cameras used to detect fires on oil rigs, can record car number plates and criminals' faces while also recording data of the size, heat and speed of the developing blaze.

Emergency Services Minister and architect of the initiative Nathan Rees said if the trial was successful, another five would be located at high points across Sydney to cover the metropolitan area.

The cameras could also be rolled out across the State in high population areas to act not only as early warning devices for bushfires but as evidentiary weapons in the fight against arson.

Premier Morris Iemma said it was a much needed weapon to catch what appeared to be a growing number of arsonists.

``This new system has been specially designed to automatically detect smoke plumes, using recognition software that does not require an operator,'' Mr Iemma said.

``Once a fire is detected by the cameras, the system sounds an alarm and firefighters are alerted.

``The camera can then zoom-in on the blaze to locate and monitor the flames.

``If there are suspicious people or vehicles nearby, high resolution images can be captured to assist police and fire investigators.''

Police have revealed that a juvenile is being ``legally dealt with'' every five days in NSW for lighting a fire.