Ylva Johansson warned that "criminal elements" usually take advantage of big migratory flows.
There is a "huge risk" that Ukrainian children and women fleeing the war may fall victim to human trafficking, the European Union's Home Affairs Commissioner warned on Monday.
"We have seen few reports of trafficking, but I have to tell you that this is really a concern. We know that we have a lot of orphans in Ukraine. We know that we have children being left, that being born by surrogate mothers that have not been picked up by their parents," Ylva Johansson told reporters during a visit to Estonia.
"There is a huge, huge risk of vulnerable children being trafficked or being victim of forced adoption. We all know, we know from experience that when we have a big flows of migration, there is always people taking advantage of the situation and using and taking on women and vulnerable women and children as a victim for trafficking," she added.
Nearly 3.5 million people have left Ukraine since Russia started its invasion on 24 February, according to UN data. Over two million have gone to Poland with another 1.2 million going to other neighbouring countries including Romania, Moldova, Hungary and Slovakia. About half of the refugees in Poland are children.
Johansson said that "very few unaccompanied minors (are) being registered."
But she stressed that there have been "quite alarming reports" from NGOs and Ukrainian women's organisation that have flagged that some women have gone missing.
"The big majority of those that are picking up people on the EU side of the borders are there to help genuinely in any solidarity. But there are always some criminal elements that try to sneak in and to use this opportunity. They say "we are offering a shelter to women and children" and then that turns into something else and people are in a very vulnerable situation," she went on.
To prevent a possible major increase, the European Commission has activated its network of anti-trafficking coordinators.
"We should not wait until we have proof of a lot of trafficking, because then it might be too late."
On the issue orphans and babies born to surrogate mothers in Ukraine, she stressed that "the most important right now is to rescue the children and to make sure that they will be protected and to be taken care of in an orderly way."
"I'm pretty worried about the situation where these orphanages can be, where the staff can, can leave because of the dangerous situation, or the children can be actually victims of bombings or things like that."