Metropolitan Police Commissioner Bernard Hogan-Howe said he believed the helicopter was being diverted to a nearby heliport when it crashed.
"The top of the crane was actually obscured by fog so I didn't see the impact," Michael Gavin told the BBC. "But I heard a bang and saw the body of the helicopter falling to the ground along with pieces of the crane and then a large plume of smoke afterwards."
The area, roughly 10 blocks from the major Waterloo train and Underground station, is extremely congested during the morning rush hour.
