A new, social media-fuelled controversy is aggravating tensions between Hong Kong and China, which has ruled the territory since 1997. Footage emerged online last week of an incident in which a toddler - the child of mainland Chinese tourists - was seen urinating in a Hong Kong street.

In the video, an angry, hectoring crowd in Mong Kok, a packed shopping district popular with Chinese tourists, surrounds the family, causing the child to cry. The parents try to grab the memory card of someone in the crowd who had filmed the child. People in the crowd shout at the family in Cantonese, as the parents respond in Mandarin. The mother was reportedly arrested for allegedly slapping someone.

Hong Kong protesters during an anti-mainland tourist rally in Hong Kong's Mong Kok in March. Credit:Reuters

The video went viral, playing to the long-standing frustrations of Hong Kong residents who resent the influx of mainlanders into their city. Hong Kong's commerce secretary used the occasion to urge residents to calmly teach their mainland brethren better manners, a statement that, while aimed at being conciliatory, smacked of condescension.

Every year, some 30 million to 40 million Chinese tourists visit Hong Kong, which maintains its own immigration and customs controls. In the past, Hong Kongers have rallied against all sorts of perceived Chinese invasions: from pregnant mainlanders taking up space in hospitals to Chinese shoppers buying up Hong Kong-produced infant formula (rather than risk potentially tainted supplies on the mainland).