Beijing: Hong Kong police have arrested six men believed involved in an attack by triad gangs on commuters at Yuen Long train station after a major public backlash over initial police inaction.

The men were identified from online video and security cameras as being among 100 thugs dressed in white shirts who hunted and hit democracy protesters returning from a march with metal poles and canes on Sunday evening.

The men were arrested for illegal assembly but police said more charges could follow.

Men wearing white shirts were filmed wielding rods and beating demonstrators at Yuen Long MTR station in Hong Kong on Sunday.

The South China Morning Post reported several of the men "had triad backgrounds", and that members of Wo Shing Wo and 14K triads were involved in the attack, in which 45 people were injured.