Christian charities are warning that children fleeing the conflict in Ukraine could be exposed to heightened risks of violence, exploitation and abuse.
Christian social policy charity CARE predicts a "disturbing spike in cases" in months to come, as Europe faces mass displacement of Ukrainian citizens seeking refuge.
The charity, which lobbies for greater protections in law for victims of trafficking, is calling on governments across Europe to "step up efforts" to spot and prevent crime given the situation.
International Christian children's organisation World Vision is also warning of the detrimental psychological impact the crisis in Ukraine will have on children and families.
The United Nations says more than 800,000 civilians have fled Ukraine, but the European Union estimates that up to four million people may try to leave the country because of the Russian invasion.
Refugees are fleeing to neighbouring countries such as Poland, Romania, Slovakia, Hungary and Moldova.
The UN estimates at least 160,000 have been displaced within their own country, but that figure is expected to rise.
World Vision plans to provide psychological first aid for children who have been traumatised by the conflict, alongside relief supplies for refugees.
Eleanor Monbiot OBE, World Vision's regional leader for Middle East and Eastern Europe, said:
"We are genuinely concerned about the growing humanitarian and psychological needs of the children and families most affected by the crisis in Ukraine. The situation is changing rapidly, but we are seeing in Ukraine, as we have seen in other conflicts around the world, that there is a growing psychological impact.
"Due to this, as well as distributing aid packages, World Vision is on the ground in Romania and planning a cross border response in Moldova to prepare essential support to refugees. We will start by providing practical things like water and other supplies, but we are also looking at offering psychological first aid to children and individuals arriving from Ukraine.
"Building on our significant local expertise in Romania, we will also be supporting educational continuity for children. In conflict situations the world over we have found that this helps to restore a sense of normality and create better coping mechanisms during what might very well become a protracted crisis.
"We are growing increasingly concerned about the real possibility of children being separated from their parents and families during displacement. Children forced to flee their homes, and especially those then without the protection of a caregiver, are incredibly vulnerable to exploitation and violence.
"The children and families impacted by this conflict need urgent support, and we are calling on people to help by donating to World Vision's Ukraine crisis response."
Lauren Agnew, human trafficking policy expert at CARE, commented:
"The situation in Ukraine is hugely alarming for those working to combat human trafficking. Governments across Europe must be mindful of the added dangers we now face. Current EU estimates put the number of displaced Ukrainians at over 7 million.
"People fleeing the conflict are arriving in Poland, Romania, Hungary, Moldova, and Slovakia. We know that criminal gangs are operating in these nations, waiting to traffic people across Europe and into the hands of exploitative industries, including in the UK.
"Traffickers prey on the vulnerability of displaced individuals, who they see as an opportunity to turn a profit. A crisis like Ukraine is a business opportunity for criminals. We expect a disturbing spike in cases.
"We call on UK Ministers to recognise the acute risk of exploitation the people of Ukraine face as they flee war and step-up efforts at home and abroad to challenge this heinous industry."
World Vision has asked for prayers for those affected by the conflict.