Parts of Hong Kong's metro system ground to a halt on Saturday as skirmishes from the day's protesting spread to the subway, with footage showing images of people being beaten as they cowered on the floor behind umbrellas.

Police notified they arrested 40 people inside Prince Edward metro station on suspicion of obstructing officers, unlawful assembly and criminal damage. Three stations stayed shut on Sunday.

"A large group of protesters participated in unlawful assembly in various districts since yesterday, despite police’s objection and warning," police said in a statement. "The level of violence is rapidly escalating and their illegal acts have no regard to the laws of Hong Kong."