Stretching across India, Pakistan, Nepal, China and Bangladesh, the "brick belt" is a vast area containing hundreds of thousands of kilns that produce countless bricks.

But behind the walls of many of these kilns are slaves - men, women and children forced to work against their will, with no pay and no way out.

They work under the threat of violence, in hot and dusty conditions. If they try to escape, their employers often claim they have debts to repay, forcing them to return.

Chandravati and her four children aged between nine and 20 work at a brick kiln every day. Her children sometimes work at night so they can attend school.

"The owner abuses us, the contractor also abuses us. He says that he doesn't have money. We are all hungry, our kids are hungry!" she says.

Now activists and academics are using space technology to find the kilns likely using slavery.

Researchers in Britain are using satellite imagery to look for the distinctive buildings, pits and chimneys that signify an active brick kiln with many labourers.

"All of these things give us an idea of the prevalence of slavery activity, bonded labour happening in the kilns," says Dr Doreen Boyd, one of the researchers.

Once they find a kiln they suspect is using slave labour, the researchers contact local NGOs who help rescue the workers.

101 East explores how satellite imagery is exposing modern slavery.

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Source: Al Jazeera