HONG KONG (AFP) - Stay and endure a life of privation and oppression or escape and risk being sold into sexual slavery: this is the stark choice facing many women in North Korea, best-selling author and activist Hyeonseo Lee warns.

The daughter of a military official, she is not your typical defector - it was curiosity not desperation that pushed her to venture beyond its borders. Almost 20 years on, she has become a powerful voice of dissent, laying bare the reality of life under the totalitarian regime in her memoir The Girl With Seven Names.

Now she is campaigning for greater protection for North Koreans who manage to flee - particularly women - warning that many are captured in China and sold into prostitution or end up in forced marriages.

"All but the lucky few will live the rest of their lives in utter misery," she told Agence France-Presse. "They will be repeatedly raped day in and day out by an endless supply of customers who enrich their captors at their expense."

Horrified by "survivor testimony", she is launching a new NGO, North Star NK, which has agents in the field across South-East Asia and China helping those trafficked in the sex trade to escape.

Ms Lee says: "They are so humiliated and broken, they don't want to speak out, so I decided I should try to help."

The Tumen and Yalu rivers act as a border with China. In some parts, the water is navigable, while in winter they are frozen over completely. For many, the physical act of crossing is the easiest bit.

There is no asylum once they reach the other side. They are regarded as illegal migrants and face deportation if caught and then severe punishment in North Korea.

The women are in an incredibly vulnerable position, Ms Lee says. They have little choice but to trust the brokers smuggling them out. But there is no one to turn to if things go wrong.

"North Korean women and girls run a gauntlet of forced marriage, and sexual abuse, in China as a de facto requirement to escape to a third country," says Mr Phil Robertson, deputy director of Human Rights Watch in Asia.

Ms Lee herself narrowly avoided being forced into the sex trade when she crossed into China. She was told she was being trained to work in a hair salon but on arrival she discovered it was a brothel, and managed to run away.

North Korean women are also trafficked as "forced brides", she says, usually sold to men in the countryside. The combination of China's one-child policy and a historic preference for boys has now led to a shortage of women of marriageable age. Families are willing to pay hundreds of dollars for brides for otherwise ineligible bachelors.

This too can end in abject misery.

"One trafficked woman I know was severely beaten by her husband and his family. To prevent her from escaping, they chained her inside a shed when they weren't monitoring her," Ms Lee recalls.

"Some of these trafficked North Korean women commit suicide, while others hold onto a sliver of hope that they will eventually escape. Almost none of them succeed."

Her own story is one of remarkable survival against the odds.

From public executions and corpses lying on the streets to family gatherings and playing with friends, Ms Lee's memories of her childhood are a patchwork of the ordinary and the horrifying - and yet, she says, it was all normal in North Korea.

"The sad truth for most North Koreans is that they are brainwashed to think that their complete lack of freedom and human rights is normal," she says.

For her, the coil of indoctrination unravelled gradually. She grew up on the border - the neon lights of China visible just across the Yalu River.

"My country was completely dark, even though we were supposedly superior," she explains. "Living so close to China also allowed me to secretly watch Chinese TV channels, which opened my eyes to a whole new world."

A nationwide famine, known as the "Arduous March", also forced her to reconsider the rhetoric of the regime.

"In my hometown of Hyesan I could see dead bodies on the streets. The smell of decomposing flesh made me feel sick and gave me goosebumps," she recalls.

It is estimated hundreds of thousands died.

Ms Lee was just 17 when she crossed illegally crossed the river into China, planning on just a short visit. Instead she ended up on a decade-long odyssey, during which she assumed multiple identities, evaded state crackdowns on North Koreans, and endured betrayals and beatings.

She says: "I've had many low points throughout my life, but I remember crying so much when I was living by myself in China, because I never thought I would see my family again. I hated myself."

In 2008, she arrived in Seoul and was granted asylum, before going on to guide her family from North Korea to freedom too. She is happily married to an American, whom she met in the city.

Now she is determined to use her experiences to bring about change.

She says: "It's essential that the people who have been oppressed speak out. It's the most effective way to compel the international community to help."