Security has already been stepped up on the New York subway

The city has awarded a $212m (£118m) contract to defence firm Lockheed to run the security programme for the bus and the underground train network.

The upgrade will also include enabling mobile phone signals on the subway.

The authorities said concerns that this could help the detonation of bombs were outweighed by potential advantages.

These include the ability of passengers to make emergency phone calls from 277 of the 468 underground stations.

Pivoting cameras

More than 1,000 cameras and 3,000 sensors will be installed at platforms, stations and terminals, on bridges and in tunnels, but not in train carriages or buses themselves.

The cameras are said to be able to capture images from 100m (300ft) and to zoom, pivot and rotate.

Sensors will be able to detect non-moving objects left on a platform.

It is not clear how long the installation will take, but according to reports the first cameras are already being installed.

The announcement of the programme comes more than six weeks after four suicide bombers killed 52 people in attacks on London's transport network.

Deterrent

New York authorities have been criticised for being slow to protect their own network - the country's biggest - despite having cash at their disposal.

The Metropolitan Transportation Authority (MTA) approved a $591m (£330m) security plan in 2002, but until now has only spent a fraction of that.

"We hope (this) will detect the terrorists before an incident happens, not just be able to report for forensic purposes after an incident happens and identify who the terrorist is," MTA Executive Director Katherine Lapp said.

"If a person were to put an unattended package... this system hopefully would identify it and we would be able to respond, to deploy our bomb sniffing dogs or emergency personnel in order to take that possible explosive device out of the system."