There is growing discomfort with the way neighbourhood watch members use race to profile people they deem "suspicious".

A Facebook spat between residents of Harfield Village, a middle-class neighbourhood in Cape Town's southern suburbs, revealed that many were approaching black people and asking them what they were doing there.

One resident had made a citizen's arrest of someone he found suspicious, but police released the man for lack of evidence.

Police spokeswoman Angie Latchman urged residents not to post information on social media that is "unsubstantiated, as this is causing undue fear in the community".

Media Monitoring Africa director William Bird said the growing trend of using the codes "bravo" (black) and "Charlie" (coloured) in social media group alerts was problematic.

"It really wouldn't help identify a possible perpetrator. It would be like saying 'a white male in Norway'."

The website Suburban Fear, set up this week to expose racism and hate speech in neighbourhood watches, had more than 15000 page views within a few hours.

"The page was inspired in reaction to a spate of racist incidents stemming from the southern suburbs in Cape Town," said the creator, who asked not to be named for fear of victimisation.

In Westdene, Joburg, Bridget van Oerle tried to get a protection order against a neighbour who had "verbally abused" and "threatened" her for trying to stamp out racism in the neighbourhood watch.

"He called me late one night on my landline and said: 'You have started a war. I am the king of Westdene and I am going to take you down.'"

The police advised her to get a protection order, but the magistrate could not grant it because the man had not physically sat outside her house. She accepted the ruling.

Isobel Frye, director of the Studies in Poverty and Inequality Institute, said the trend of making people feel that certain areas were off limits to them because of their race was "a bizarre new form of influx control".