NEW DELHI — The girl’s screams were brittle and desperate. Neighbors in the suburban housing complex looked up and saw a child crying for help from an upstairs balcony. She was 13 and worked as a maid for a couple who had gone on vacation to Thailand. They had left her locked inside their apartment.

After a firefighter rescued her, the girl described a life akin to slavery, child welfare officials said. Her uncle had sold her to a job placement agency, which sold her to the couple, both doctors. The girl was paid nothing. She said the couple barely fed her and beat her if her work did not meet expectations. She said they used closed-circuit cameras to make certain she did not take extra food.

In India, reported to have more child laborers than any other country in the world, child labor and trafficking are often considered symptoms of poverty: desperately poor families sell their children for work, and some end up as prostitutes or manual laborers.

But the case last week of the 13-year-old maid is a reminder that the exploitation of children is also a symptom of India’s rising wealth, as the country’s growing middle class has created a surging demand for domestic workers, jobs often filled by children.