The incident happened outside the Tuen Mun Town Hall after a large number of demonstrators fled to Tuen Mun Road.
In the footage, a large number of protesters dressed in black are seen fleeing. In the melee, some protesters wrestle down an officer who was holding one suspect.
Then others join in a mass attack at the officer who was down on his knees. A large number of riot police officers then rush to save the officer, who manage to hold on to the detained man.
Officers and protesters had clashed in Tuen Mun at several spots after a march sanctioned by police was brought to an early close due to chaos.