A photograph of a masked policewoman in plain clothes sitting on a 14-year-old schoolgirl after she pinned her to the ground at a busy road junction in Hong Kong on Wednesday has gone viral, sparking criticism online.

The girl, who was in school uniform, was one of four secondary students who were arrested at the junction of Ma Tau Wai Road and Tam Kung Road, in To Kwa Wan, at about 7.15am.