"So we came back with more [officers], but by that time she was already gone. That haunted me because you see the horror of what happens to a person in the cycle and can't get out."

Now project director of Liberty Asia, a Hong Kong-based alliance of professionals dedicated to tackling human trafficking, Friedman says it is important to recognise the issue as the modern equivalent of slavery: the victims are deceived, coerced or even abducted from their communities and transported to other places where they are cruelly exploited.

The International Labour Organisation estimates about 21 million people were trafficked around the world last year, including 11.7 million in Asia. "There are 1.1 million new victims a year, which is 3,000 victims a day, 125 per hour," Friedman says.

But his horrifying stories aren't just a concern of poor, developing countries; they occur in Hong Kong, too. In July, for example, two Thai women were lured to the city by offers of well-paid jobs as masseuses, and then threatened with violence and forced to work in a Yau Ma Tei brothel.

Their ordeal came to light after the pair escaped and managed to call an NGO in Bangkok, which sought help from Thai consulate officials here.

Although it is hard to get a good grasp of the numbers, NGOs such as Caritas Hong Kong, Zi Teng and Christian Action have all helped victims of human trafficking.

For Christian Action, the most recent case was 12 women from the Philippines who were brought to Hong Kong last year with promises of work as domestic helpers, but wound up in Wan Chai bars.

"Over the years, we are seeing more and more labour trafficking," says Christian Action manager Lisa Lee Yuen-ling.

Lee recalls meeting a young Indonesian maid who not only owed large debts to employment agencies after being duped into paying them substantial fees, but was also raped by each of her male employers in Taiwan, Malaysia and Hong Kong. The woman was eventually sent back to Jakarta - not her hometown - without any money or resources. Lee doesn't know what has happened to her.

"These 'headhunters' look for girls in villages with little education, or who are illiterate, and arrange jobs for them - for a fee," Lee says. "The pretty ones have it the hardest."

Hong Kong is both a destination and transit station for syndicates, which are smuggling people to other cities in the region, law enforcement officials say.

In recent years, many victims have ended up in Macau, due to the rapid expansion of resorts and casinos. Friedman has observed a similar trend, noting cases of young Mongolian women being trafficked through Hong Kong to Macau.

Yet, until a month ago, Hong Kong officials did not recognise trafficking as a concern; statistics were not being collected to gauge the extent of the problem, strategies were not being devised to help victims.

However, the US State Department report on Trafficking in Persons (TIP) for 2013 has described Hong Kong as "a destination and transit territory for men, women and teenage girls from mainland China, Colombia, the Philippines, Indonesia, Thailand, Vietnam, Nepal, Cambodia, and elsewhere in Southeast Asia, subjected to sex trafficking and forced labour".

The TIP report sorts countries into three categories. Tier 1 countries comply fully with minimum standards set under the US Trafficking Victims Protection Act. Hong Kong is listed as a Tier 2 destination - one which is not in compliance but where the government is making significant efforts to improve. Tier 3 countries make little effort to protect trafficking victims.

According to Michael Vidler, a solicitor who has been active on human rights issues, this puts Hong Kong on the same level as countries such as Serbia, Ukraine, Egypt and Cambodia.

"If we don't start to change things, we're going to end up on the TIP watch list, which includes Turkmenistan, Afghanistan, South Sudan, Albania and Liberia," he told a seminar on sexual violence and sex trafficking hosted by the Department of Justice last month.

Countries are placed on the watch list for the year if there is evidence of severe forms of trafficking or if numbers increase significantly and authorities fail to bolster efforts to combat trafficking through more vigorous investigation and prosecution of offenders, and providing greater assistance to victims.

Then director of public prosecutions Kevin Zervos, who spearheaded the seminar, says he began to look seriously into the issue of trafficking in 2011, examining how other countries dealt with law enforcement and prosecution.

But first, Zervos says, "we had to recognise we had a problem, that Hong Kong is not exempt from this global concern".

"We would look into individual cases to see if it was exploitation, but they were classified by the criminal offences under which they were charged, such as sexual assault, false imprisonment and prostitution," he says.

A presentation by government counsel Catherine Ko Po-chui at the seminar showed there were 4,604 arrests for prostitution in 2010, with the number dropping to 3,618 last year, and 1,900 arrests in the first seven months of 2013.

However, local groups dealing with trafficked victims believe the number of sex workers arrested represents only a fraction of the trafficked women being forced into prostitution, and that there are many more who are not in the judicial system.

Between 20 and 30 people are in court every day for breaching their stay in Hong Kong and many were probably trafficked into the city, Vidler says.

But Zervos is confident that better data will be collected in the coming months to provide a more accurate picture.

Under Hong Kong law, trafficking is still narrowly defined as crossing the border for prostitution. However, it is making progress in tackling the issue with the Department of Justice recently amending its Prosecution Code to include human exploitation cases, bringing it in line with the UN's Palermo Protocol on human trafficking, which has been ratified by 157 countries.

"This is a code for prosecutors on how to approach these cases, giving them principles and criteria on how to prosecute, explaining their duties and the requirements that need to be met," Zervos says.

"Our action plan includes data analysis and then looks at the law and how the legal system is dealing with it to see what changes need to be made. Then we monitor the progress and look for other ways to deal with underlying problems.

"We don't want to just treat the symptoms, but understand the problem and direct our efforts to the root cause of it."

Instead of prosecuting the victims of trafficking, Zervos argues that the department should encourage them to testify against traffickers and provide them with counselling and support in being repatriated to their home countries.

Friedman has been hugely encouraged by the big step forward that Hong Kong has taken with Zervos' announcement.

"When I came here three years ago, the judicial department would say 'Hong Kong is a location with a strong rule of law. We have no human trafficking here.' But when you have strict immigration laws, the trafficking goes underground. It's the same in Singapore and Tokyo. However, the problem is out in the open in Cambodia and Bangladesh, because there isn't much rule of law.

"When you start to realise the possibility of trafficking, then you start looking for it."

Worldwide, just 4,000 people were prosecuted for trafficking last year, he says, with 50,000 reported cases of trafficking out of 21 million.

The profits from trafficking are estimated at US$32 billion, compared to just US$350 million spent to address the problem.

"Hong Kong is fresh to the topic, but it also has 20 years of experience to lean on from other countries," Friedman says.

"Hong Kong has the potential to be the model for the region because it considers itself a just city and many groups are available to help. Now it needs to move the process forward."