An ancient Cambodian city lost for more than 1,200 years has been found by archaeologists using airborne laser technology.

Details of the city of Mahendraparvata, near Cambodia's famous Angkor Wat Buddhist temple complex - the largest such complex in the world - was discovered using laser technology known as Lidar (light detection and ranging), which penetrated the thick forest vegetation to discover the hidden city beneath.

Laser scanning mapped out the area, enabling archaeologists to discover a previously undocumented formal urban planned landscape of canals, buildings and roads.

The discovery was announced in a peer-reviewed paper released by the Proceedings of the National Academy of Sciences journal.

University of Sydney archaeologist Damian Evans, the study's lead author, said: "No one had ever mapped the city in any kind of detail before, and so it was a real revelation to see the city revealed in such clarity.

"It's remarkable to see these traces of human activity still inscribed into the forest floor many, many centuries after the city ceased to function and was overgrown."

Mahendraparvata was found atop Phnom Kulen mountain in Siem Reap province, about 25 miles (40km) north of the Angkor complex.

The laser technology used by the archaeologists works by firing laser pulses from an aircraft to the ground and measuring the distance to create a detailed, three-dimensional map of the area.

Evans said: "What we have now with this instrument is just 'bang' - all of a sudden, an immediate picture of an entire city that people didn't know was there before, which is remarkable.

"Instead of this kind of very long gradual process, you have this eureka moment where you bring the data up on screen the first time and there it is - this ancient city very clearly in front of you."

The reserarchers said the structure of Mahendraparvata was similar to modern cities.

Roland Fletcher of the University of Sydney, said: "It's the same sort of configuration as Los Angeles - a dense middle, but it consists of huge, sprawling suburbs connected by giant roads and canals in exactly the same way as the freeways link up Los Angeles."

Evans added. "To see the extent of things we missed before has completely changed our understanding of how these cities were structured."

Researchers said the next step will be to excavate the site to help give clues to how many people lived in the city.

It is thought the civilisation at Mahendraparvata collapsed after their canal and reservoir systems failed.