Some 246 million children between the ages of five and 17, or one child in every six in the world, work and about 75 per cent of them have hazardous jobs, the International Labour Organisation (ILO) said today.
In its most detailed report yet on the problem, the UN agency said the Asian-Pacific region had the largest number, with 127 million children aged between five and 14 having a job.
Despite the increasing commitment by governments and their partners to tackle child labour worldwide, it remains a problem on a massive scale, said ILO Director-General Mr Juan Somavia.
The ILO said it was particularly alarmed at the fact that such a high number - about 180 million - were trapped in what it called the worst forms of child labour where they could be exposed to health risks or physical injury.
Most such jobs were in agriculture or mining but they could include slavery and prostitution.
It estimated that 8.4 million children were caught in the unconditional worst forms of labour - slavery, trafficking, debt bondage and other kinds of forced labour, forced recruitment for armed conflict, prostitution, pornography and other illicit activities.
"Despite significant progress in efforts to abolish child labour, an alarming number of children are trapped in its worst forms," it said.
The ILO said that at 206 million, the overall figure for the number of children under 15 in work in developing countries was down on the 250 million figure usually quoted.
In many countries it is legal to work from 15, but there are still international agreements limiting the tasks that can be done.
However, the reduction in the developing country figure could be just a reflection of the improved data-gathering methods used since the ILO last made a study in 1995, it warned.
Although Asia had the highest total number of child workers, the incidence was greatest in Africa where an estimated 41 per cent of children worked.
The ILO said about 30 per cent of African children between the ages of 10 and 14 were employed in agriculture, despite the fact that most African countries had ratified international pacts against child labour.
There were seven million child labourers in Brazil, with 20 percent of all girls between the ages of 10 and 14 working as domestic staff in Brazil, Colombia and Ecuador.
But the practice is not limited to the developing world. Some 2.5 million children, or one per cent of the world's child labourers, are employed in rich countries. Another 2.4 million are found in the transition economies of eastern Europe.
The ILO's Minimum Age Convention of 1973, which sets 15 as the limit, has been ratified by 116 countries around the world, while 117 states have adhered to the 1999 Convention on the Worst Forms of Child Labour.