More than three-quarters of children and young adults trying to migrate to Europe across the Mediterranean are victims of abuse on the dangerous journey, according to a UN report published today.

Children's rights agency UNICEF and the International Organisation for Migration said young migrants coming from sub-Saharan Africa were particularly at risk from abuse.

The UN agencies surveyed 22,000 migrants and refugees including 11,000 children and young people.

Their report says 77% of children and young people trying to cross the Mediterranean to Europe had suffered "direct experiences of abuse, exploitation and practices which may amount to human trafficking".

"The stark reality is that it is now standard practice that children moving through the Mediterranean are abused, trafficked, beaten and discriminated against," Afshan Khan, UNICEF Europe regional director, said in a statement.

"Those originating from sub-Saharan Africa are far more likely to experience exploitation and trafficking than those from other parts of the world" it said.

"Racism is likely a major underlying factor behind this discrepancy."

The main migration route from Libya is particularly dangerous due to lawlessness, militias and criminality, it said.

Young migrants pay the equivalent of between €800 and €4,000 for the journey, only to arrive in Europe in debt and facing new risks.

The UN accused the EU last week of turning a "blind eye" to the brutality faced by migrants held in Libya and called for urgent action to help them.

Europe continues to struggle with the biggest migration crisis in its history, fed initially by refugees in Syria but now with the central Mediterranean route from Africa coming back into play.