“The reality is that we are not going to meet the MDGs unless child labour is systematically adressed,” UNICEF expert Kate Donovan told a press conference in Geneva on the eve of a global conference on the issue.

Progress in areas such as improving education and tackling poverty, gender inequality and HIV by 2015 have been “systematically undermined by child labour”, she said.

Donovan said current UN figures, which show there are around 150 million children aged between five and 14 involved in child labour, have “massively underestimated” the true scale of the problem.

“Migrant children, orphans, girls and those included in invisible labour, including domestic labour and sexual labour are missed consistently by current data,” she added.

UNICEF said the problem was worst in Africa, with around one child in every four being involved in child labour.

Solving the problem was “very complex” and required a combination of work and social protection initiatives to help the most vulnerable children get access to basic services.

The UN set a 15-year timeframe at the turn of the millennium to achieve its goals of halving extreme poverty, boosting health and education and further empowering women across the developing world.