The aid worker, who asked not to be named, is currently helping Ukrainians at the Medyka border crossing in Poland.

He described the human trafficking problem as “rampant” and said that every day different charities radio around to warn others of suspicious men sighted in the area.

The fear is that these men are snatching children to sell on to criminal gangs and forcing women into slavery and prostitution.

“The most alarming story from site that I have heard is that two men were caught by the Polish army and they had women in the back of their van,” he added.

“The Polish military got the women out and moved the men to the Polish police. At this point, the men bribed the Polish police and they were released without charge or without having their details taken. This was viewed by more than one member of charity organisations.” HuffPost UK has approached Polish police for comment.

Such stories are not uncommon. There have been reports of children going missing and multiple cases of human trafficking reported by aid groups.

“Sadly, as in all armed conflict, trafficking gangs have emerged,” says Anna Dabrowska who is also helping Ukrainian refugees in Poland.

“As soon as people started fleeing Ukraine, there were a number of men spotted in the main train station of Wroclaw.”

Dabrowska, director of human rights at the NGO Homo Faber, said the men were approaching women with children offering them safe accommodation in Germany.

Suspicious, the women asked police for advice and the men quickly disappeared from the station.

HuffPost UK has heard multiple accounts of men trying to traffic desperate young female refugees fleeing the war in Ukraine.

Amid the chaos of war, it is impossible to tell exactly how many women or children may have already fallen victim to these criminal gangs. And experts say the full scale of what is taking place might not be realised for years – if ever.

The United Nations believes that around 10 million people have fled the fighting and Russia has been accused of genocide amid reports that civilians have been “abducted and taken to camps”.

Unaccompanied children are increasingly arriving at border points, in what is becoming the largest refugee crisis in Europe since WW2.

There are harrowing reports of sexual violence against women emerging from Ukraine’s frontline and the prosecutor general claimed last week that 103 children had been killed.

As civilian casualties and atrocities soar, women face the unenviable decision over whether to stay or flee with their children.

However, the more desperate they become, the easier it is for those with nefarious intentions to prey on them.

“For predators and human traffickers, the war in Ukraine is not a tragedy,” Secretary-General of the UN António Guterres recently commented. “It’s an opportunity – and women and children are the targets.”

Shabia Mantoo from the United Nations High Commissioner for Refugees [UNHCR] said they were “gravely concerned” about reports of trafficking and were helping governments to scale up prevention measures.

This includes encouraging neighbouring countries to establish vetting systems or procedures for those offering support to refugees.

“I think 90 per cent of the refugees fleeing Ukraine are women and children,” Mantoo told HuffPost UK.

“In situations of mass displacement it is unfortunately expected that women and girls can be at a heightened risk of gender-based violence, and also vulnerable to the risks of exploitation and abuse, including trafficking.”

Charity workers on the border say that only since Sunday has the Polish government started doing checks on them, adding: “Until that point no-one was checked by police, anyone could drive up to the point where refugees were about to get on to the bus.”

As thousands of vulnerable refugees poured over the border, traffickers have been promising women and children safe transport and accommodation.

Hillary Margolis, a senior researcher at Human Rights Watch, said she heard such reports from the Slovak border.

She said the hungrier and weaker refugees become, the more likely it is that they will end up in unsafe situations.

“People will do things that they might not think they would do because they’re literally starving, need medical care and a place to stay,” she added.

Lauren Agnew, human trafficking and sexual exploitation policy officer at charity Care, said human traffickers see the crisis as a “business opportunity”.

She described the situation as a “recipe for human trafficking” and warned that refugees fleeing Ukraine were crossing into countries that were already “hotspots” for the criminal enterprise.

Agnew added: “Human traffickers will be waiting in the wings in these countries, ready to take advantage of this humanitarian crisis and to exploit vulnerable individuals for profit. They know that refugees will have a lack of options and may be inclined to accept dangerous offers of assistance.

“The refugees are desperate to get across the borders and it’s likely that traffickers may approach them, offer to help with transport just across the borders and then later order that they pay vast amounts of money for that journey, which forces them into debt with these criminal gangs.”

This is echoed by charity workers who say some refugees have had to spend hours in temperatures well below freezing.

The anonymous charity worker in Poland added: “There have been numerous incidents of exposure to the elements requiring serious medical attention for Ukrainians anywhere between the age of two weeks up to very elderly.

“On top of this, there is no shelter, or benches, or chairs between the two borders so fatigue plays a huge role in the problems.”

He said it was hard for refugees to work out the good from the bad, adding: “There are volunteers arriving from all around the world with no affiliation to any charity. There are hundreds of people trying to help and this makes it especially dangerous.

“As the refugees walk through what I described as the ‘gauntlet of kindness’ they are bombarded with food, drink and sweets so it is easy for someone nefarious to pose as someone doing good.

“For example I reported two strange looking men giving out sweets to kids the other day.”

It comes amid reports of refugees suffering from frostbite, having to melt snow to drink and displaying symptoms of PTSD.

Trafficked people can be forced into labour, commercial sexual exploitation and domestic services. Before the war, women were already trafficked from Romania to the UK for sexual exploitation.

Shawn Kohl, from the International Justice Mission [IJM], stressed that established trafficking networks already exist in countries where the refugees are arriving such as Poland, Romania, Bulgaria and Hungary.

From there, victims are often trafficked onwards into Western Europe, including the UK. “This current crisis widens the pool of potential victims,” Kohl said.

He added: “Traffickers can recruit vulnerable people either in person or online, by offering work or to meet other needs, such as shelter.

“Once an individual has been recruited, threats and coercion can be used, for example, by taking their passport, to ensure the victim stays under the control of the trafficker.

“Victims are often trafficked outside of the country they have been recruited in, for exploitation in another country.”

Aid workers say they believe multiple criminal gangs are operating on the borders, however they also warn about “opportunistic” individuals.

It comes after a man was arrested in Poland on suspicion of raping a refugee at a camp by allegedly luring her in with the offer of shelter after she had just escaped from Ukraine.

A major concern for many of the charities is unaccompanied minors – those who have travelled alone or have been temporarily separated in the chaos.

The United Nations Children’s Fund, Unicef, has warned that the conflict in Ukraine is a child protection crisis.

They say that more than 500 unaccompanied children were identified crossing from Ukraine into Romania from February 24 to March 17. Although the true number of separated children who have fled Ukraine to neighbouring countries is likely much higher.

Unicef has activated “Blue Dot” one-stop safe spaces that provided crucial support to families on the move.

They have particular concerns for the 100,000 Ukrainian children who live in institutional care – nearly half of which have disabilities.

The Ukrainian government has issued clear directives to all childcare facilities, including orphanages, on how to organise their evacuation if needed.

They include instructions that they must travel with as much documentation as possible, and the requirement to notify Ukrainian services when they arrive in a neighbouring country.

Margaret Banjo, child protection specialist from Unicef, said: “You can already imagine that if you don’t have your legal guardian or you’re moving alone as a child in this, then you become more vulnerable to protection issues. Whether it is gender based violence, whether it is child exploitation, child labour and trafficking.”

Banjo said that the generosity of those who want to help could sometimes provide cover for those who have “ill motives”.

She said child traffickers could easily blend in, so they have issued advice for formal volunteers which includes not leaving children with someone claiming to be their parent.

Guillaume Landry, from children’s rights charity Ecpat, said: “With so many fleeing and seeking to escape the war, our concern is that criminals will capitalise on the chaos and use it as an opportunity to prey on young children who have been separated from their families.”

Landry, executive director of Ecpat, said authorities needed quicker access to verify the background of those wanting to help and added: “It is important that we are able to get to a place where we are able to quickly identify at-risk children and have referral pathways to prevent them from being lured into the clutches of exploitation or trafficking rings.”

Asked about cases of human trafficking by HuffPost UK, Ukrainian MP Maria Mezentseva said: “There are facts of child trafficking let’s say or human trafficking, which are now taking place. We have the Prosecutor General’s office who’s dealing with it together with national police.

“There is a clear letter from our government on the children not to be crossing from instance from orphanages.”

Mezentseva was one of four Ukrainian MPs who were given special permission to visit the UK last week.

During the visit, the MPs accused Russian forces of raping women over 60 years old before hanging them and said Putin’s strategy was to target women and children.

If it is any consolation, some on the ground say that checks on the identity of workers on the Polish border have been stepped up, but conceded: “Many thousands of people have slipped through the cracks.”

They also report an increased security and police presence on the border.

However, plenty stress that damage has already been done and some of those who have been trafficked will end up in the UK.

Robyn Phillips from the Human Trafficking Foundation, a UK-based charity, said they were watching closely what was unfolding in Ukraine.

She said: “With trafficking we often just think of sexual exploitation but actually it’s forced labour in any any form. That could be manual construction, farming, hospitality even.

“There’s also domestic servitude, so exploiting people within the home, criminal exploitation as well so forcing people into committing crimes, whether that’s drug cultivation or robbery and also organ harvesting as well.”

Recently former Tory prime minister Theresa May raised concerns over human traffickers in the House of Commons.

The Maidenhead MP warned that it was happening in Poland, adding: “It’s a sad reflection on human nature, that the very point where these women and children are fleeing Ukraine for their safety to find refuge elsewhere, the criminal gangs have moved in to make money from the trafficking of what they consider to be yet another commodity, that is human beings, and they are attempting to make money out of this human distress and vulnerability.”

Layla Moran MP, Lib Dem spokesperson on foreign affairs, said we must do all we can to protect people fleeing Putin’s “war machine”.

She added: “We know that the best way to keep refugees out of the hands of human traffickers is to provide safe and legal routes to sanctuary. The government must uphold our proud tradition of welcoming those in need.”

A Home Office spokesperson said: “The government is committed to tackling the heinous crime of human trafficking.

“We are keeping the situation in Ukraine under review and remain in close contact with the Ukrainian government.”