The scene is eerily familiar. The camera angle is not. A cloud of smoke and ash billows above Manhattan after terrorists hijacked two airliners and flew them into the upper floors of what was once America’s tallest building.

A collection of images taken from police helicopters above New York on the morning of 11 September 2001 was made public yesterday, providing some of the first detailed birds-eye views of thecollapse of the World Trade Centre. NYPD photographer Greg Semendinger was responsible for many of the most striking shots on a day when almost all other air traffic was grounded.