This includes human trafficking, forced labour, forced or servile marriage, and the sale and exploitation of children.
New Zealand is estimated to have 600 people in modern slavery, the fourth lowest prevalence of 167 countries in the Global Slavery Index.
The known cases involved workers in modern slavery with the most widely documented being on fishing charter vessels in New Zealand waters, Ms David told NZ Newswire.
"Their situations have included being subjected to violence, sexual abuse, being fed stale bread and fish bait, working 30-hour shifts and even being paid 35 cents an hour."
New laws clamping down on fishing boat conditions come into force in 2016, which was "really positive", she said.
The government's response to slavery was ranked 27th out of the 167 countries, with laws in place which protected against most forms of modern slavery, Ms David said.
However, the government could do more to ensure crimes acts offences that exist get the full effect, she said.
"There probably needs to be more training and more awareness-raising for law enforcement agencies.
"They may even need support of how to handle these very complex cases of foreign victims, because this is just not usual run of the mill policing."
New Zealand should also review its action plan on human trafficking last reviewed in 2009, she said.
"It's hard for every government to keep up with the changing patterns in criminals. Criminals can act quickly, governments of course have to follow proper processes."
The annual report measured prevalence through sources, including random surveys in 19 countries, secondary sources from 58 countries and pre-existing surveys.
Results were estimated for other countries considering factors including vulnerability, geography, and country context.
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