2,500 men, women and children live tents surrounded by rivers of mud on the site
Jeremy Corbyn has described conditions at an organised French refugee camp near the Channel Tunnel as "shameful" and "much worse" than he expected.
Mr Corbyn made his comments as he visited Dunkirk on his first foreign visit as Labour leader.
The British Labour Party leader was mobbed by families of mainly Kurdish refugees as he walked around the Grande-Synthe Camp where 2,500 men, women and children are living in tents surrounded by rivers of mud next to a sports stadium near Dunkirk.
Mr Corbyn told Sky News he was trying to draw attention to the plight of families from war-torn countries attempting to reunite with relatives in Britain.
He said: "What I'm trying to achieve here is to understand the nature of the refugee crisis that's facing the whole of Europe.
"Ultimately we deal with the situation by dealing with the problem at its source, which are the wars and conflicts.
"Also, there are the human needs of people. We have got people here who have been here for months, if not longer than that, with no proper education, no access to doctors, no access to dentists, limited access to food - in very cold, very wet conditions.
"These conditions are a disgrace anywhere. We as human beings have to reach out to fellow human beings."
Car loads of volunteers from the UK and France were distributing sleeping bags, clothes and food in awful conditions, particularly for hundreds of very young children.
He called on the Government to accept more unaccompanied children immediately and join efforts to share refugees around the European Union.
It comes as EU officials prepare to meet to discuss suspending Europe's border-free travel zone drawn up under the Schengen agreement, for two years.
French prime minister Manuel Valls warned the refugee crisis put the future of the European Union, whose key principle is the freedom of movement of people between countries, in "grave danger".
He told the BBC: "It's Europe that could die, not the Schengen area. If Europe can't protect its own borders, it's the very idea of Europe that could be thrown into doubt.
"It could disappear, of course – the European project, not Europe itself, not our values, but the concept we have of Europe, that the founding fathers had of Europe.
"Yes, that is in very grave danger. That’s why you need border guards, border controls on the external borders of the European Union."
Speaking at the World Economic Forum in Davos, International Monetary Fund chief Christine Lagarde warned that the influx of migrants had pushed Europe to "make or break point", which put the Schengen agreement under threat.
As he left the camp, a refugee with baby son interrupted a Sky News interview to ask Mr Corbyn for help after his child's dangerous loss of weight.
Mr Corbyn said he would investigate the case of some British passport holders who approached him saying they were living in the camp trying to get passage for their families.
The number of migrants at the Dunkirk camp has risen from 800 in October to 2,500 in recent weeks, most of whom are from Syria and Iraq.
The Government has helped fund French efforts at the camp, after a deal announced in August.