The City of Cape Town's decision to establish a special vice squad would leave real criminals untouched, sex workers' advocacy organisation Sweat said on Thursday.

"Far from sex workers being criminals, they are in fact among the main victims of crime," said Sweat director Eric Harper.

He was responding to an announcement by mayoral committee member for safety and security JP Smith that the "long overdue" squad would crack down on the city's red light areas.

The unit has already begun arresting and fining sex workers.

However Harper said Smith confused cause and effect when he said sex work was associated with other forms of crime.

"When sex work is made illegal, it is driven underground and regulated by criminals," he said.

"On the other hand when sex workers are allowed to operate openly, they have proved, here and in other parts of the world, to play a valuable service assisting the police to fight crime."

Sex workers in one part of Cape Town, for example, had created an informal neighbourhood watch which, among other things, resulted in the arrest of a murder suspect.

Sex workers were easy targets and were useful in helping the police raise their arrest figures.

But this only diverted attention from other far more serious issues ? including widespread violence against women.

"Sex work will not go away," Harper said.

"What will occur with councillor JP Smith's action is that it will be more difficult for mothers to put food on the table for their children and pay school fees."