A video of a marathon in Chongqing, China, has gone viral after a low-flying helicopter blew billboards into the leading pack, injuring at least one runner.

The helicopter flies across the road, but then disappears off screen when the camera lens is turned on to the runners. While other runners file down the other side of the road, a group of elites comes rushing up behind the pacing van

At that moment, the helicopter, which can still be heard, blows all the advertising across the road. The boards crash into the leading pack and they are forced to push them out of the way to continue.

One runner appears hurt and tries to limp his way back into the race.