Black child prostitutes walking the streets of Pretoria at night sell their services mainly to married white professionals, a recent study has found.

Presenting the findings to a conference on child labour in Pretoria on Tuesday, the researchers urged the government to act immediately.

They said the clientele of black prostitutes mostly comprised white men in their late forties.

"The interviewees claimed that most of their clients were married and held professional occupations, such as those in the public sector, law, business sector and education."

The prostitutes questioned were between 13 and 18 years old.

One was quoted as saying: "These clients take us to their houses or flats and one can see their status by just looking at their furniture. They also have certificates which reflect their educational level."

The research was undertaken in a joint project by Willem Schurink of the Human Sciences Research Council and Sam Tshabalala and Choarelo Molope of the Centre for Human Rights at the University of Pretoria.

It focused on various forms of child labour, including prostitution, and minors working in brickyards, on farms and at taxi ranks.

The researchers concluded that certain types of child labour were abusive and should be abolished.

"Child prostitution and hazardous working conditions are unequivocally harmful and exploitative, and the government is urged to take immediate corrective action."

The child prostitutes, who charged the researchers about R80 for a 40-minute interview, are from townships around Pretoria and work in the city centre and certain spots in Pretoria West.

"They did not ply their trade on Sundays because, first, because they believed it to be a sin to sell sex on a Sunday," the research report said.

Most of the girls were runaways. Others had left their homes and gone to the city because of social and economical problems at home.

Turning to other forms of child labour, the researchers said they came across boys as young seven working at a brickyard in Mpumalanga. Some earned R100 a fortnight for loading 400 bricks a day on a truck barehanded.

The most disturbing finding from a survey on farm labour, the researchers said, was that many children working in the agricultural sector were illegal immigrants. Some suffered ill-treatment from farmers.

A Zimbabwean youngster told how five white farm workers assaulted him and four other workers in September last year.

"He said they were assaulted with pick-axe handles and shocked with an electrical device used to shock cattle," the researchers said.

They recommended that child labour such as farm work be strictly regulated to protect children who had to work to survive.