Nearly 30 million people are living in slavery across the globe, many of them men, women and children trafficked by gangs for sex work and unskilled labour, according to a global slavery index.

The index, released on Thursday by anti-slavery charity Walk Free Foundation, ranked 162 countries on the number living in slavery, the risk of enslavement, and the strength of government responses to combating the illegal activity.

It found that 10 countries accounted for 76 percent of the 29.8 million people living in slavery - India, China, Pakistan, Nigeria, Ethiopia, Russia, Thailand, the Democratic Republic of Congo, Myanmar and Bangladesh.

Modern slavery was defined as human trafficking, forced labour, and practices such as debt bondage, forced marriage, and the sale or exploitation of children.

Researcher Kevin Bales said he hoped the index, the first annual report to monitor slavery globally, would raise public awareness as numbers were at an all-time high and it would increase pressure on governments to take more action.

Blame corruption

He dismissed the view that poverty was the key factor behind slavery and instead blamed corruption, calling for laws to stop organised gangs.

"Consistently when we analysed the statistics we found that corruption came out as more powerful than poverty in driving slavery," said Bales, a professor of contemporary slavery at the Wilberforce Institute for the Study of Slavery and Emancipation at the University of Hull in northern England.

"Fundamentally this is a violent crime issue."

The report found Mauritania in West Africa had the highest number of slaves proportionately, with up to 160,000 enslaved in a population of 3.8 million, due to culturally-sanctioned forms of chattel slavery and high levels of child marriage.

The highest absolute numbers were almost 14 million in slavery in India and 3 million in China.

"By far the largest proportion of this problem (in India) is the exploitation of Indian citizens within India itself, particularly through debt bondage and bonded labour," said the report.

In China there was forced labour of men, women and children, including domestic servitude and forced begging, sexual exploitation of women and children and forced marriage.

Coming last in the index were Iceland, Ireland and Britain although Bales stressed they were not slavery-free.

Up to 4,400 people are estimated to be enslaved in Britain, the victims mainly from Africa, Asia and Eastern Europe.

They are forced into sex work, domestic servitude, or low-paid jobs in agriculture, construction, restaurants and nail salons.

"Hopefully this report will be a wake-up call for rich countries as well," Bales told Reuters.