Nearly 30 million people around the world are living as slaves, according to a new index ranking 162 countries.
The Global Slavery Index 2013 says India has the highest number of people living in conditions of slavery at 14 million.
But Mauritania has the highest proportional figure with about 4% of its population enslaved.
The report’s authors hope it will help governments tackle what they call a “hidden crime”.
The index was compiled by Australian-based rights organisation Walk Free Foundation using a definition of modern slavery that includes debt bondage, forced marriage and human trafficking.
“A lot of governments won’t like hearing what we have to say,” WFF chief executive Nick Grono told the French news agency Agence France-Presse.
“Those governments that want to engage with us, we will be very open to engaging and looking at ways in which we can better measure the issue of modern slavery.”
I urge leaders around the world to view this index as a call to action, and to stay focused on the work of responding to this crime”
The organisation’s estimate of 29.8 million slaves worldwide is higher than other attempts to quantify modern slavery. The International Labour Organisation estimates that almost 21 million people are victims of forced labour.
India, China, Pakistan and Nigeria have the highest numbers of people enslaved, the charity said.
Together with five other countries, they account for three-quarters of the total estimated number of people in modern slavery worldwide.
The report said India’s ranking was mostly due to the exploitation of Indians citizens within the country itself.
While the highest proportion of slaves is in Mauritania, with many people inheriting slave status from their ancestors, Haiti is second in the index and Pakistan is third.
The new survey has the backing of world figures including former US Secretary of State Hillary Clinton, ex-British Prime Minister Tony Blair.
Mrs Clinton said that although the index was not perfect, it provided a starting point, according to the Associated Press.
“I urge leaders around the world to view this index as a call to action, and to stay focused on the work of responding to this crime.”