"While the information vacuum poses challenges, we are confident that the data reflects the most accurate estimation on the pervasiveness of modern-day slavery inside North Korea", said Ms Fiona David, Walk Free's executive director of global research, noting that the research had also involved looking at a variety of pre-existing data from worldwide organisations and non-profit organisations.
Eritrea and the Central African nation of Burundi were also found to have a high prevalence of slavery.
India was found to be home to the largest total number of slaves, with an estimated eight million among its 1.3 billion population.
Researchers interviewed 50 North Korean defectors who spoke of long hours and inhumane conditions in forced unpaid labour for adults and children in farming, construction and road building.
A rights foundation says modern slavery in developed countries is more common than thought.More news: Illness forces Marchionne out of Ferrari
The findings indicated two key drivers of modern slavery: "highly repressive regimes, in which people are put to work to prop up the government, and conflict situations which result in the breakdown of rule of law, social structures, and systems of protection".
"These people simply were born in the wrong place, and that's why they're being punished for-their birthplace", said Park, who has founded a group help North Korean trafficking victims.
But the source also said North Koreans desire unification.
The government estimated in 2013 that only about 13,000 people in Britain were modern-day slaves - trapped in forced labour, sexual exploitation and domestic servitude - while the police have said there are likely to be tens of thousands.
The report was compiled by the Walk Free Foundation, an anti-slavery campaign founded by Australian billionaire Andrew Forrest, who said at the NY press conference that "for the first time there is real hope we can end modern slavery".More news: Spain: Judge drops extradition bids for 6 Catalan fugitives
"For example, we know that criminals involved in these types of exploitation are going into online spaces to enable their criminality", the NCA's deputy director added in a statement.
"UN agencies warned of the risk of modern slavery in this chaotic and high-risk environment".
The report cites coal, cocoa, cotton, timber and fish as among the products that may be tainted by modern slavery. The report says slavery is increasing in Australia and some European nations.
The group recommends making forced marriage illegal, creating a minimum marriage age of 18, a national database of trafficking and forced labor cases, and working to improve supply-chain transparency to help bring the U.S. numbers down. Vietnam was the second-largest source ($11.2bn), with India ($3.8bn) third. The report noted gaps in data from Arab states, as well as a lack of information on organ trafficking and the recruitment of children by armed groups.
There are more female than male victims across all forms of modern slavery.More news: CVS fires pharmacist who wouldn't fill transgender customer's prescription