Congolese children were kidnapped, taken to an orphanage and put up for adoption in Belgium after their parents were tricked into sending them to a holiday camp, it has emerged.

Belgian prosecutors have officially asked "about 15" families for DNA samples from their adopted children in a bid to trace their biological parents. The adoptive families had thought the biological parents were dead.

“This is a drama. How do you explain such things to those children? Not to mention the pain that real parents must feel in the Congo", Lorin Parys, a Flemish politician with an adopted son, told the Het Nieuwsblad newspaper.

The DNA demand applies to all Congolese children adopted in Belgium from November 2013 and comes as an 18 month investigation builds up a head of steam.

Prosecutors want the tests to find out the extent of the trafficking in Congolese children to Belgium, which infamously colonised a region including the present day Democratic Republic of Congo.

Investigators have identified at least four cases where a Congolese child adopted in Belgium had living biological parents thousands of miles away. The parents, who lived in the countryside, were convinced to send their children to a holiday camp in the capital Kinshasa.