More than 70,000 children across Asia are being used by sex tourists, mainly in Cambodia, Indonesia, the Philippines and Thailand, an independent expert said Thursday.

Frans van Dijk of Dutch aid group Terre Des Hommes Netherlands told AFP on the sidelines of a conference here that the numbers of children working in the sex tourism trade was on the rise.

"It's difficult to work out the real number but we are sure that the reality is much more" than estimates of 60,000 to 70,000, he said at the three-day Southeast Asia Conference on Child Sex Tourism.