GUNFIRE echoed through downtown Los Angeles for a training drill.
Counter- terrorism police demonstrated a response to a weapon of mass destruction threat – all while curious pedestrians watched on.
The drill began with an explosion of flash grenades, officers firing blank ammunition at pretend suspects, and police rappelling out of a helicopter and onto a hotel bridge.
A truck carrying a barrel soon drove onto the scene, presenting the challenge of neutralising an improvised explosive device in the centre of a highly populated area.
Police Chief Charlie Beck said: "This is something we constantly worry about. The threat is always there."