Out of 167 countries New Zealand had the fourth lowest number of people in slavery.

New Zealand has an estimated 800 people living in modern day slavery, an international slavery survey says.

The 2016 Global Slavery Index examines practices such as forced labour, human trafficking, child exploitation and forced marriage, surveying 43,000 people in 25 countries.

The number of people living in slavery in New Zealand has increased from 600 in the 2014 Global Slavery Index.

New Zealand and Australia have the lowest level of slavery prevalence in the Asia Pacific region with an estimated 0.018 per cent of the population in modern slavery.

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The report says while countries like Australia and New Zealand have strong policies around slavery, some minority groups, including migrants, are at risk of exploitation.

Don Lord, chief executive of human trafficking and slavery awareness organisation Hagar, said slavery was increasing in New Zealand especially amongst migrant workers.

Slavery was most common in New Zealand's fishing, dairy, agriculture, construction and hospitality industries.

"All of these are prone to labour exploitation," Lord said.

It was often difficult for people who had suffered forms of trafficking and exploitation to come forward and speak about their situation, he said.

"They're often vulnerable people who have come from overseas who need their job."

If New Zealanders suspected cases of slavery they should contact the Human Rights Commission, he said.

New Zealanders should also be thinking about the goods they purchased to ensure they came from "clean" supply chains.

"It's definitely something we as New Zealanders need to become more aware of, we need to learn more about it and make conscious decisions."

Some companies in New Zealand, like The Warehouse, were working hard to ensure their supply chains did not involve slavery.

The 2016 index again found Asia, which provides low-skilled labour in global supply chains producing clothing, food and technology, accounted for two-thirds of the people in slavery.

Australia, with a population of 23.7 million had an estimated 4300 people in slavery.

Out of 167 countries New Zealand had the fourth lowest number of people in slavery.

Only Barbados, Iceland and Luxembourg had fewer people in modern slavery.

However, New Zealand was ranked 52 out of 167 countries for slavery prevalence.

The Government's response to slavery was rated BB, second for the Asia Pacific region to Australia, which had a BBB rating.

Of the 25 countries within the Asia-Pacific region Australia, New Zealand and the Philippines had the strongest responses to modern slavery with strong victim support services, specialised law enforcement units and laws, policies and programmes that address cycles of vulnerability.

The index, which is published by Australian mining billionaire Andrew Forrest's Walk Free Foundation, found that almost 60 per cent of the world's slaves are in five countries: China, India, Pakistan, Bangladesh and Uzbekistan.

Forrest was using the report to lobby leaders of the world's largest economies - United States, China, Japan, Germany, Britain, France, Brazil, Italy, Russia and India - to enact legislation on supply chain transparency for all goods and services imported or sold in their countries.

Forrest found "abhorrent" forced labour practices in the supply chains of Fortescue Metals' - a company he was chairman of.

He had ordered an audit of the company and warned that other corporations and governments would find the same if they looked.

"Businesses that don't actively look for forced labour within their supply chains are standing on a burning platform," Forrest said.

In the report modern slavery referred to situations of exploitation that a person could not refuse or leave because of threats, violence, coercion, abuse of power or deception, with treatment akin to a farm animal.

It included human trafficking, forced labour, slavery and slavery-like practices and forced or servile marriage.