Almost 46 million people are living as slaves globally with the greatest number in India but the highest prevalence of slavery in North Korea, according to the third Global Slavery Index released on Tuesday.
The index, by Australia-based human rights group Walk Free Foundation, increased its estimate of people born into servitude, trafficked for sex work, or trapped in debt bondage or forced labor to 45.8 million from 35.8 million in 2014.
Andrew Forrest, founder of Walk Free, said the rise of nearly 30 percent was due to better data collection, although he feared the situation was getting worse with global displacement and migration increasing vulnerability to all forms of slavery.
Incidences of slavery were found in all 167 countries in the index, with India home to the largest total number with an estimated 18.4 million slaves among its 1.3 billion population.
But North Korea ranked as worst in terms of concentration with one in every 20 people - or 4.4 percent of its 25 million population - in slavery and its government doing the least to end this with reports of state-sanctioned forced labor.
"We need to make it clear we're not going to tolerate slavery and when there is slavery in a regime we should not trade with them," Forrest, an Australian mining billionaire and philanthropist, told the Thomson Reuters Foundation.