Following a mission to the country, François Crépeau, the UN special rapporteur on the human rights of migrants, said the EU’s “absence of long-term vision” and “clear lack of political will” had caused suffering.

“This is not only a humanitarian crisis,” he said. “This is more importantly a political crisis in which the EU and the overwhelming majority of member states have abandoned Greece – a country that is fighting to implement austerity measures – leaving it to deal with an issue that requires efforts from all.”

Crépeau criticised the closure of borders surrounding Greece, such as the border with Macedonia, and the deal brokered between the EU and Turkey.

The controversial EU-Turkey agreement entails the deportation of migrants who have made the perilous journey across the sea to reach Greece back to Turkey – a move critics, including the UN’s refugee agency (UNHCR), argue is a breach of human rights and international law.

Instead of reducing the number of those seeking refuge in Greece, Crépeau said the amount of irregular migrants in the country had exponentially increased.

“Unlike before, Greece is no longer a transit country and is struggling to catch up and develop a mechanism to deal with immediate needs, in the absence of a clear commitment from the EU to support the country.”

He raised concerns about the length of the process of identify vulnerable migrants, “blatant” over-crowding, the mixture of people stuck in close quarters, contradictory and confusing information and weak safeguards in detention facilities.

He highlighted the EU-backed ‘hot spots’ – centres set up to identify refugees among the thousands of migrants arriving every day on Greek islands – which have become de facto closed detention centres for those who are to be returned to Turkey.

Crépeau said these are creating “unacceptable” levels of “confusion, frustration, violence and fear” since the EU-Turkey deal was agreed.

The European Commission maintains that reception conditions in Greece are the responsibility of the Greek authorities.

However, a spokesperson said the EU is working to improve these and tackle issues in hotspot centres, including those related to unaccompanied children and other vulnerable groups.

The commission has earmarked millions of dollars in funds for the Greek authorities and NGOs working to manage the crisis, which it claims will provide essentials like food, health care and shelter to tens of thousands of refugees.

But critics say Greece needs more substantial support to cope with the crisis. The commission has offered just over €500m worth so far, with some of that yet to be delivered.

Meanwhile, the UN’s refugee agency has also warned that a huge shortfall in funds for sheltering refugees is hampering efforts to handle the biggest displacement crisis since the Second World War.

It has launched a new campaign to help plug the half-a-billion dollar deficit and ensure adequate shelter for refugees.

The Nobody Left Outside campaign hopes to see shelter improved for 2 million vulnerable people by 2018 and is appealing to the private sector, individuals, foundations and philanthropists.