UN High Commissioner for Human Rights Louise Arbour, speaking at an Asia-Pacific human rights conference in Beijing, called trafficking in humans horrendous.
"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," she said.
The International Labour Organisation estimated more than 2 million people were trafficked worldwide every year, the head of the UN children's agency Unicef said.
"No country or region is immune," Unicef executive director Ann Veneman said.
"Children are forced into prostitution, begging and soliciting, labour on plantations and in mines, markets, factories and domestic work."
In the Asia-Pacific region, especially in Southeast Asia, the sex trade is a major factor behind the smuggling of people.
Girls from poor villages in Myanmar, Cambodia, the Philippines and elsewhere are lured into cities or neighbouring countries and end up at massage parlours or karaoke bars, or are flown as far as Australia, Japan, South Africa and the United States to be kept as slaves in brothels.
Poor children are lured into hard
labour, begging and sex slavery
Arbour urged countries in the region to ratify international human rights agreements to combat trafficking.
In China, the world's most populous country, trafficking of people is a common practice of gangs that have grown alongside government corruption and widespread poverty, academics say.
The sale of women and children is a nationwide problem, partly a result of stringent government rules on family planning that allow couples to have only one child.
Security was tight on Tuesday outside the Beijing hotel where the symposium is being held, apparently to prevent any disgruntled petitioners from approaching Arbour.
China's human rights record is widely criticised, not only for issues related to trafficking, but also for the government's close grip on the media, harsh methods for maintaining order and repression of religion.
Chinese state councillor Tang Jiaxuan met Arbour before the symposium and later called on Asian countries to improve human rights, while repeating China's standard line.
"Every country should choose its own way to protect human rights according to its national situation"
Chinese state councillor
"Every country should choose its own way to protect human rights according to its national situation," Tang told representatives from 37 governments at the meeting.
"We have no other choice but to make the realisation of the right to development and the promotion of economic, social and cultural rights our most pressing task," he added, noting two-thirds of the world's poor lived in the Asia-Pacific area.
China defends its rights record on grounds that feeding and clothing its 1.3 billion people is a basic human right and more important than political freedoms.