Almost 30 million people around the world live as slaves and nearly half of them are in India, a global index on modern slavery released on Thursday said.

The Global Slavery Index 2013 said India had 14 million people living in conditions of slavery, the highest number worldwide. West Africa’s Mauritania had the highest prevalence, with 4.2 per cent of its population enslaved, the report said.

The study by the Walk Free Foundation, an Australia-based rights group, estimates 29.8 million slaves worldwide, using a definition of slavery that includes debt bondage, forced marriage and human trafficking.

The study could help governments assess and eradicate slavery, which is a “hidden and diverse” crime, Walk Free said.

“Today some people are still being born into hereditary slavery, a staggering but harsh reality, particularly in parts of West Africa and South Asia,” said the report, which ranks 162 countries.

“Other victims are captured or kidnapped before being sold or kept for exploitation, whether through ‘marriage”, unpaid labour on fishing boats, or as domestic workers. Others are tricked and lured into situations they cannot escape, with false promises of a good job or an education.” According to the report, 10 nations account for 76 per cent of the world’s enslaved. China had the second-largest number with 2.9 million slaves, followed by Pakistan with 2.1 million, Nigeria (701,000), Ethiopia (651,000), Russia (516,000), Thailand (473,000), Congo (462,000), Myanmar (384,000) and Bangladesh (343,000).

Walk Free’s estimates exceed other surveys on slavery. The International Labour Organisation estimated last year that almost 21 million people were victims of forced labour globally.

While India’s ranking was due to the large-scale exploitation of the country’s citizens, particularly through debt bondage and bonded labour, Mauritania faced the scourge due to “deeply entrenched hereditary slavery”.

After Mauritania, Haiti and Pakistan have the highest proportional figures.

Iceland has the lowest prevalence of slavery, with fewer than 100 slaves. Countries that follow Iceland with low slavery levels are Ireland, Britain, New Zealand, Switzerland, Sweden, Norway, Luxembourg and Finland.