Police have arrested a 46-year-old man after he allegedly attacked two people defending a so-called "Lennon Wall" set up in Kowloon Bay.

A video circulating on social media showed a middle-age man punching a younger man several times in a pedestrian walkway where colourful notes in support of the anti-extradition bill movement have been posted on the walls.

The older man was also suspected of earlier attacking a 65-year-old man.

It's said the incident happened shortly before 1am.

Two injured men were sent to United Christian Hospital for treatment and were said to be in a stable condition.

Police said the 46-year-old had been arrested on suspicion of assault occasioning actual bodily harm.

Earlier in the night, scuffles also broke out outside Yau Tong MTR Station when several government backers attempted to remove notes that had been posted there.

Police officers were called in to separate the crowd, with officers raising warning flags at one stage.