About 45.8 million people around the world are trapped in modern slavery, a charity said Tuesday — almost a third more than it estimated two years ago.

The Walk Free Foundation's Global Slavery Index said that India has by far the largest number of modern slaves, 18.35 million, followed by China with 3.39 million and Pakistan with 2.13 million.North Korea was found to have the highest per capita rate of modern slavery, with 4.37 percent of its population affected.

The report — launched at a London event hosted by actor Russell Crowe — ranked 167 countries by the number of people affected by practices included forced labor, debt bondage, forced marriage and sexual exploitation.

The total of 45.8 million is 10 million more than the group estimated in its last report in 2014.

Walk Free Foundation Chairman Andrew Forrest said the level of slavery hadn't necessarily increased, but more data was available.

"My gut feeling is that it is actually increasing still and it will be a year or two before it turns around," he said. "But it is going to turn around, the way the world is waking up to it.

"We're going to look back on 2016, 2015, and see that's where it all started to change, that's where India started to move aggressively against slavery," he said.

He urged nations to follow the lead of Britain, which has passed a tough law against modern slavery, with penalties of up to life imprisonment for keeping people in servitude.