Across Asia, corruption and slavery form bitter web

"Factory owners have been driving production costs down and slavery is a short-cut to that," he said. "If you're not doing it, your competitor down the road probably is."

That theme was echoed in India, Pakistan and Nepal, where kiln owners have also sought to increase profits by turning to forced labor, said Aidan McQuade, director of Anti-Slavery International in London, who has visited slave brickworks in Nepal.

But if the workers rescued from Shanxi were scarred and emaciated from their experiences, the houses of some of their captors appeared little better than the average in the dusty villages where kilns have sprung up.

Across Asia and other poorer regions, rural slave exploiters tend to be not much richer than their victims, said Bales.

"If you had a lot more money you'd just leave there," he said. "It's reflecting people who have got some power and are able to take advantages of the resources they have to exploit other people."

(Additional reporting by Jonathan Allen in New Delhi, Adhityani Arga in Jakarta, Robert Birsel in Islamabad)