New footage of 9/11 attack on World Trade Centre guardian.co.uk

Previously unseen footage of the 9/11 attacks, filmed from a police helicopter hovering above the burning World Trade Centre, has emerged almost a decade after the terrorist atrocity.

The New York Police Department air and sea rescue helicopter was dispatched to the scene of the attack to see whether any survivors could be rescued from the rooftops.

However, as the audio track proves, its crew quickly realised the enormity of the situation below.

"The whole tower, it's gone," one officer is heard yelling. "Holy crap, they knocked the whole fricking thing down."

Another officer asks: "How could it go down?"

The video is part of a cache of information about the attack handed over by city agencies to the National Institute of Standards and Technology, the federal agency that investigated the collapse.

It was released by NIST on 3 March under a Freedom of Information Act request, but it remains unclear who published the footage online.

Although many of the scenes in the 17-minute video are familiar, it provides a chilling aerial view of the burning twin towers and the cloud of smoke and dust that covered the city.

Only police helicopters were allowed in the airspace near the skyscrapers, with the officers gaining exclusive images from above. The helicopter flies over the roof as huge grey clouds billow up, and then moves away, with the video panning out to lower Manhattan. A sea of people can be seen fleeing the area.

The helicopter eventually lands across the harbour from the towers and the camera pans into the aircraft, showing the ropes that would have been used to rescue people. The sparse audio gives an indication of the raw shock experienced by its crew.

"We got out of there at the right time," one officer can be heard saying.

"I know," another replies.

The helicopter crew watches as the north tower falls in the distance, the video zooming in to capture the building's collapse and a huge plume of smoke puffing up.

"Holy shit," an officer says.

Still images from police helicopters were released to the public last year under a similar request.