This is the moment a man dangling out of a train door in South Africa slaps an unaware commuter standing on the platform.

Video filmed at Kaalfontein station in Gauteng shows the packed Metrolink train from Johannesburg to Tembisa pulling away from the station.

Out of nowhere, an unknown man reaches out and lands a slap on the commuter's face.

The filmer claimed slapping is a "common" occurrence.