Poor families in the Philippines are pushing their children into performing live sex online for paedophiles around the globe in what one senior UNICEF official calls a form of "child slavery".
"There's no limit to how cruel and gross this business is -- and it's a billion, billion-dollar business," said Lotta Sylwander, head of the UN children's agency UNICEF in the Philippines.
She called for internet providers to "get on board" in tackling the crime and said money transfer centres should do far more to identify abusers by tracking suspicious payment patterns.
UNICEF says the Philippines is the No.1 global source of child pornography and the "epicentre of the live-stream sexual abuse trade".
Sylwander described how children as young as five or six are forced to perform several times a day in front of a webcam, for an hour at a time, as buyers in different time zones come online.
"It's facilitated by mothers and fathers or close relatives. It may even happen in their home," she added. "It's definitely child slavery because the child has no choice."
The paedophiles transfer money and then give instructions of what they want to see. In many cases the child is abused by someone outside the family but there have been cases of parents abusing their own children or children abusing each other.
Sylwander said the Philippines received 7000 reports of cybercrime a month, half of which related to child sex abuse.
"Our biggest hurdle is not the government, not the police; it's getting the internet providers to come along and say we will help you track (and) stop this," she told the Thomson Reuters Foundation in an interview in London.
"My biggest concern is why don't the internet providers do more -- how can the dark web continue to do what it does?"
Sylwander said the live-streaming of child sex had boomed in the Philippines because of the high level of English, good internet access and well-established money transfer systems that Filipinos working overseas use to send earnings home.
Poverty is a driver with many parents expecting their children to contribute financially. One group of young children rescued in Manila said they were paid 150 pesos (NZ$4.70) to take part in shows.
But Sylwander cited other darker forces at work. Researchers in the Philippines who are carrying out a major survey on violence against children, to be published later this year, have found shockingly high levels of sexual abuse within families, she said.
There is also a legacy left over from the huge prostitution industry which grew up around the American military bases until they closed in the 1990s.
Sylwander said this had led to a tolerance of prostitution and when the Americans departed the industry had to find other ways of operating.
UNICEF, which works with centres that have rescued children, says they were often left severely disturbed.
Despite the rising number of cases coming to light there have been very few convictions.
One problem is that the age of sexual consent in the Philippines is 12, another is the mass of contradictions between laws. There is also no law yet around online crimes, Sylwander said.
Sylwander said UNICEF was working closely with police from Britain, Australia and the Netherlands to tackle the crime.