There are approximately 2.4 billion minors around the world who are aged below 18 years.

Nearly 138 million of these children – about one in 17 – are engaged in child labour, including 54 million in hazardous work that endangers their health and safety, according to estimates by the International Labour Organization (ILO) and UNICEF.

On World Day Against Child Labour, Al Jazeera takes a look at the latest numbers on child labour, the industries where it is most prevalent and the countries and regions bearing the heaviest burdens.

Children doing hazardous jobs

In 2015, the United Nations set a goal to end child labour worldwide by 2025. That deadline has now passed. Although the total number of children in child labour has declined, two in five of those children still work in hazardous jobs that often involve heavy physical labour, exposure to toxic chemicals, dangerous machinery, long hours, or unsafe environments.

Of the 54 million in hazardous work:

• 10.3 million (about 1 in 5) are aged 5-11
• 12.8 million (about 1 in 4) are aged 12-14
• 30.8 million (about 4 in 7) are aged 15-17

UNICEF and the ILO warn that such work can cause injury, illness and lasting damage to a child’s physical and mental development. Many of the children doing these jobs are also missing out on school, trapping families in cycles of poverty that can span generations.

Child labour in different industries

Agriculture remains the world’s largest employer of children, accounting for 61 percent of all child labour cases. That means roughly 84 million children are working on farms, fisheries, forests and livestock production.

Children carry heavy sacks across fields, spray crops with pesticides, descend into mines, work with sharp tools and machinery and spend long hours in extreme heat. Much of the world’s dangerous child labour is concentrated in the sector.

In many rural communities, work starts before sunrise and competes directly with schooling.

Children in service sector jobs, such as domestic work, retail and hospitality, account for 27 percent of child labour cases, while 13 percent work in industry, including mining, manufacturing and construction.

Child labour rates around the world

From cocoa fields in West Africa to rice farms in South Asia, agriculture involves child labour the most worldwide because it is often informal, family-based and difficult to regulate.

Lucia Soleti, acting UNICEF deputy representative of programmes in Ghana, told Al Jazeera that child labour remains widespread in West Africa, driven by poverty, limited access to social services and climate and economic shocks.

She explained how in Ghana, more than 1.1 million children aged between five and 17 are affected, mostly in agriculture, but also in mining, fishing and domestic work.

“It deprives children of education, exposes them to hazardous conditions and perpetuates intergenerational poverty,” Soleti said.

Sub-Saharan Africa remains the centre of the crisis, with 87 million children engaged in child labour, more than the rest of the world combined. Population growth, conflict and economic instability have offset many of the gains made in recent years.

While Asia and the Pacific have recorded the sharpest reductions, child labour remains embedded in global supply chains that produce food, clothing, minerals and consumer goods sold around the world.

Mona Aika, acting chief of child protection at UNICEF in Nigeria, said, child labour in the country cannot be addressed through training or enforcement alone.

“The slow reduction in sub-Saharan Africa is linked to multiple structural factors such as poverty, limited access to quality education, weak social protection, rural livelihoods dependent on family labour, conflict, displacement, climate shocks, population growth, informality of work and limited enforcement capacity,” Aika told Al Jazeera

“It requires stronger child protection systems, social protection, education access, livelihoods support for families, community prevention, referral pathways and sustained government-led action,” says Aika.