Witnesses say he had earlier been waving a chopper at some of them on Lung Cheung Road, where protesters had put up barricades to block traffic. Later footage showed a chopper lying on the ground.
The old man suffered wounds to his head and blood was running down his face. He became agitated and was unstable on his feet. He tried to hit one person and was then set upon by protesters, some with sticks.
The man fell to the ground and when the protesters pulled back, footage showed him lying flat on his back apparently motionless and possibly unconscious.
He was tended to by first-aiders at the scene, who called on police to come over.
Footage showed him with an oxygen mask and a monitor clipped to his finger.
He was then taken away by ambulance.
Last updated: 2019-10-03 HKT 03:30