Young girls in south India continue to be "dedicated" to village temples and then forced into prostitution despite laws banning the ancient ritual, researchers say.

The devadasi system, which involves putting a beaded necklace around girls and often leads to a life of sex work and slavery, goes unchecked in Karnataka state, according to two reports released this month.

Laws banning the practice are poorly implemented, and the rituals are now being done undercover, said the reports, published by the National Law School of India University and the Tata Institute of Social Sciences.