Human traffickers are operating on the Ukrainian border, taking advantage of the mass flow of refugees into eastern Europe, Sky News has been told.
Traffickers are taking young children to sell on to gangs in Europe and forcing desperate women, many of whom have left their partners in Ukraine, into slavery and prostitution.
Police in Romania and Poland have told us they have arrested suspects and have set up checkpoints to stop and search suspicious vehicles.
Authorities are worried many women are being trapped online, on sites like Facebook, before they even reach the border.
By the time they cross, they already have a contact to meet and it's too late to intervene.
The traffickers aren't always men.
Women are often used because they tend to raise less suspicion and are more likely to be trusted by female refugees.
A lot of the refugees arriving now, don't have family or friends to go to elsewhere in Europe, and so in their desperation just to get out of Ukraine alive, they're willing to go with complete strangers.
It is a horrific twist on an already dreadful situation.
Stefi Banu, a Romanian safeguarding officer, said: "It's women and children and they are already very tired and vulnerable.
"Romania is famous for its trafficking problem, and we just try to come with a solution to protect the children by protecting their mothers and informing them about the risk of human trafficking."
In Romania and Poland there are now campaigns at the border to warn refugees and help them if they need it.
Posters are at the crossings advising refugees not to travel with strangers and how to get help if they need it.
More than three million refugees have crossed from Ukraine in a little over two weeks - most of them women and children.
There is no way of knowing how many of those have been picked up by human traffickers - but it is happening.
