Raji speaks softly, her small, cross-legged frame fitting neatly into a plastic garden chair. "When we felt weak and couldn't work, they would beat us with metal rods," she says.

There is a cluster of rusty steel reinforcement bars sticking out of the concrete above us; it becomes clear those are the kind of rods she is talking about.

Raji thinks she was beaten five or six times during the seven months she spent in India working on building sites after being trafficked from her village in mid-western Nepal, lured by promises of a well-paid job as a domestic help. She was 16 at the time.

"It was very hard," she says. "We had to carry bricks; not just one or two, lots of bricks … you had to put the basket on your head. After that, they would put more than 20 bricks in it at one time. We carried them up two floors.

"We had to work from 6am to 7pm. We were given food twice a day. Rice, and potato in soup, and the rice was old. We were hungry."

The woman who persuaded Raji's parents to let her go to India said she would get good clothes, and meat to eat every day.

"We'd been told we would get 180 rupees [£1.37] a day. But they gave me 100 rupees just one time. We slept in the house that was being built … we just slept on the ground on thin bedcovers. Once, we tried to escape at night, but they found us and beat us."

Raji's friend Kamashi, who was 17, was taken to India at the same time together with five boys from their village. "We had to work even when we had lots of injuries to our bodies," she says. "When we asked for money to buy medicine, we were beaten even more."

Kamashi was raped by another worker and was one month pregnant when she and Raji returned to Nepal.

Indian brothels

Statistics vary on the number of Nepalese women who fall prey to traffickers, but social workers in the country estimate that about 200,000 girls and women are working in Indian brothels, with up to 7,000 more arriving every year, says Rekha Rana, co-ordinator of the combating girls' trafficking project at the Family Planning Association of Nepal (FPAN). Others are trafficked into domestic servitude.

"While trafficking into forced sex work gets most of the attention at the international level, these stories show that women and girls are trafficked into all kinds of forced labour," says Seri Wendoh, the International Planned Parenthood Federation's (IPPF) senior technical officer on sexual rights and gender.

Men are trafficked for construction work, too, but this tends to be talked about simply as "migrant work", ignoring that many end up being paid very little or nothing, Rana says.

Demand for cheap labour in the destination countries is a major driving force, but she believes a lack of employment in Nepal and political instability since the end of the civil war seven years ago are equally responsible. Low levels of education and awareness of the issue also play a role.

Women and children are most at risk: the Demographic and Health Survey for 2011 (pdf) found that only a third of women aged 20-24 had been to secondary school, and only half of those had completed their studies. Almost a quarter of girls in that age group had received no education.

In a country where travelling abroad to find employment opportunities is far from unusual – more than 100,000 women are thought to go to India every year as non-trafficked migrant workers – it is unsurprising that women are duped, especially if those offering the supposed jobs are people they know.

"Women living in an environment of restricted rights, limited personal freedom and few employment opportunities may decide migration is their only hope for achieving economic independence and a higher standard of living," Rana says.

Trafficked by relatives, friends and partners

"Trust is the key issue. Many trafficked people are victims of their own relatives, friends and partners. The agents spend time persuading young women and girls with promises of marriage, a good life, work and money. Sometimes they actually marry the girls and take them to their destinations."

It is a lucrative business: Maiti Nepal, an NGO working to prevent trafficking to India for forced sex work – and to rescue and rehabilitate survivors – says traffickers in that area can be paid upwards of 30,000 Indian rupees (£364) for every person they supply, depending on age and other factors.

It was a woman from the village who took both Raji and Kamashi away. "Our mother told the woman she didn't want Raji to go away, but the woman said there would be lots of girls going with her, so she didn't need to be worried," says Raji's older sister, Beli.

Geographically, trafficking is most prevalent in parts of Nepal that lag behind in terms of literacy, health, access to road transport, and other basic indicators, and where unemployment is high.

Most of these districts are on the 1,800km-long (1,118 miles) open border with India, which Nepalese citizens do not need travel documents or work visas to cross. Once over the border, they may be moved to other countries using forged passports; in the past decade, India has become a well-used transit route to the Gulf states and south-east Asia.

There's also a link between Nepal's long history of bonded labour and trafficking for construction work, Rana explains. Although the Kamaiya system of bonded labour was abolished in 2000, many Kamaiyas were released by their former landlords without any support.

"The Kamaiyas are now free, but they are also out of work," she says. "Since they do not have their own land, and arable land is not plentiful in Nepal, there are too many people looking for gainful employment. Pimps know these people are vulnerable and they prey on them."

Nepal has passed stringent anti-trafficking laws over the years, including its Human Trafficking and Transportation (Control) Act of 2007, and is a signatory to international conventions addressing the issue.

"Lack of laws is not problem," says Rana. "Non-implementation of laws is the core impeding factor. The government has not been intervening in this migration process or attempting to identify traffickers or people who have been trafficked."

The US state department's 2012 report into trafficking in Nepal says laws have not been well implemented, with continued incidents of "trafficking-related complicity" by government officials.

Micro-loans option

On the ground, FPAN tries to prevent poor women being tempted by traffickers' offers by awarding them micro-loans to set up small businesses that can give them financial stability. Peer educators, including trafficking returnees, work to warn others of the dangers of accepting job offers outside Nepal.

Focusing on the root causes of trafficking is crucial, Wendoh says: "It has to be an empowered approach to make these young women and their families more financially independent. Economic empowerment also enables young women and girls to become more resilient, through building their self-confidence."

There are loans for women who've survived trafficking, too, to give them a reliable income and with it raised status within their community, helping them to counteract the stigma often attached to returnees.

Raji and Kamashi managed to make it back to Nepal after Kamashi's impoverished family paid the brother of the trafficker to bring them home.

Today, Kamashi is one of eight women sharing a mushroom farm financed by a 35,000 rupee loan. Last year, they made 25,000 rupees between them; this year, they're aiming for 100,000, and plan to increase the target annually.

"I would like to do this for the rest of my life," says Kamashi. "My daughter is two now. I couldn't get any education; I cannot read. I want to provide her with an education so she will be successful. I want to give her skills so she can be independent and earn money for herself."

• Rachel Williams travelled with IPPF. FPAN is one of the IPPF's 152 member associations. Some names have been changed