Louise Arbour, the UN's High Commissioner of Human Rights, said millions of women and children were ending up as sex slaves, beggars and forced labourers because of human trafficking, and called for closer international co-operation to prevent it.
Ann Veneman, the executive director of Unicef, the UN children's organisation, said two million people were estimated to be trafficked every year. "No country or region is immune," she added.
The senior UN officials were attending an Asia-Pacific human rights conference in Beijing. China has come under intense criticism for its own human rights record, and tight security at the hotel where the conference was held was believed to be designed to prevent Chinese petitioners from approaching Ms Arbour with their own complaints of abuse at the hands of the Chinese authorities.
Human trafficking is a term for the illegal smuggling of people, not as refugees but as cheap or slave labour.
In the Asia-Pacific region, especially south-east Asia, it is a problem of epidemic proportions, and it is fuelled mostly by the sex trade.
Girls from poor villages, particularly in Burma, Cambodia and the Philippines, are lured into cities or neighbouring countries, where they are forced to work as prostitutes. They are flown abroad to work as far as Australia, Japan and the United States.
Many are lured with promises of better-paid jobs than they could ever dream of at home, and have no idea that they will end up as prostitutes. Others know they are going into prostitution, but are fooled into believing they will be paid and free to leave when they have made enough money, but are instead forced to work as sex slaves.
The problem is "horrendous", Ms Arbour said. "By its very nature, it constitutes an acute violation of human rights and reports today suggest that more people are being trafficked than ever before." Far from helping the victims of trafficking, many governments punish them, Ms Arbour said. "Often, those who are trafficked are criminalised, for example as illegal migrants or prostitutes, when they should be receiving assistance as victims."
Ms Veneman said that children were not immune from trafficking, and were forced to work as child sex slaves. "Children are forced into prostitution, begging and soliciting, labour on plantations and in mines, markets, factories and domestic work."
She told the conference that on a recent trip to Africa, she met children who had been kidnapped and heard first-hand from some girls how they had been forced to become child soldiers, and from others how they had been sold into sex slavery.
"Gender-based violence in any of its forms denies girls and women their basic rights and dignity, and harms the development of entire countries," she said.
Thirty-seven Asia- Pacific countries are attending the conference. Some observers have criticised China as an unlikely setting for a conference on human rights, given its own poor record.
A Chinese official who met Ms Arbour, Tang Jiaxuan, gave the usual Chinese government line: "Every country should choose its own way to protect human rights according to its national situation."