Thousands of refugees are enduring freezing temperatures in flimsy tents across Greece as a result of the arctic blast that has swept across Europe, triggering criticism abroad and putting the government on the defensive.

In a robust exchange in parliament the migration policy minister, Yannis Mouzalas, conceded that people trapped in the country were living in appalling conditions exacerbated by severe cold weather and unprecedented snowfall nationwide.

“The situation in the hot spots is very bad,” he said. “Conditions on the islands are awful.”

The government has faced severe criticism over conditions in reception centres, which pose health and safety risks in the depths of winter.

Footage of tents weighed down by snow in the vastly overcrowded Moria camp in Lesbos has elicited particular consternation – and embarrassment for Mouzalas, who only days ago insisted that in light of government preparations there would be no refugees living in the cold. Reports of illness among elderly and infirm refugees have been rife, with agencies attributing outbreaks of pneumonia and flu to the lack of adequate shelter.

Facebook Twitter Pinterest A man stands next to a snow-covered tent in the Moria camp on the island of Lesbos. Photograph: AFP/Getty Images

On Monday the images drew a sharp rebuke from the European commission. “The situation is untenable,” said a spokeswoman, Natasha Bertaud. “But we also have to be clear … that ensuring adequate reception conditions in Greece is a responsibility of Greek authorities.”

Temperatures have plunged to –5C on Lesbos, where authorities have struggled to cope with refugee numbers that surpassed capacity long ago. In other parts of Greece, including the southern island of Crete, the cold snap has seen temperatures drop to an unprecedented –14C. In the Attica region surrounding Athens – where efforts have been under way to place people in rented apartments – sub-zero temperatures were also recorded with snow blanketing ancient monuments.

The unusually cold readings are expected to continue through to Thursday.

On Tuesday, a flight carrying Mouzalas to Lesbos, where the United Nations refugee agency, the UNHCR, is leading efforts to move people into hotels, was turned back because of the bad weather.

“Efforts are under way to move people as quickly as possible into hotels,” the island’s mayor, Spyros Galinos, told the Guardian. “I’ve not seen so much snow, ever. Electricity supplies have been knocked out. There are villages that are isolated, without light or heating or running water. It’s difficult for everyone.”

An estimated 62,000 migrants and refugees have been stranded in Greece following the closure of borders by countries further north and Europe’s deal with Turkey to curb flows last March. About 10,000 of those are trapped on the Aegean islands, including Lesbos.

Although the number of arrivals has dropped dramatically since sea patrols were stepped up, more than 180,000 people have managed to reach Greece since March. Official figures released on Tuesday showed 5,491 refugees on Lesbos alone. Moria, the island’s main facility, was built to house less than half that number. The government’s migration spokesman, Giorgos Kyritsis, said fewer than 1,000 refugees were still living in tents on the islands.

“The burden has to be reduced,” said Galinos. “Refugees have to be moved inland to other centres on the mainland.”

Facebook Twitter Pinterest Laundry of Syrian refugees covered with snow at the refugee camp of Ritsona, north of Athens. Photograph: Muhammed Muheisen/AP

In northern Greece, where the deep freeze worsened at the weekend, the plight of refugees living in tents in abandoned industrial warehouses was further complicated by water and electricity cuts.

NGOs attributed the chaos to the absence of a national response plan, saying despite warnings of bitterly cold weather the state had been woefully ill-prepared.

But international organisations also said the shocking images highlighted Europe’s inhumane policies towards refugees and migrants.

“What we are seeing on the islands is the manifestation of the way Europe is failing to provide dignity for some of the world’s most vulnerable,” said Panos Navrozidis, country director of the International Rescue Committee in Greece. “It is imperative that people are moved off the Greek islands. The IRC warned of these life-threatening conditions months ago yet still now with this weather we face a life-or-death situation.”

Facebook Twitter Pinterest Pictures of Moria under a blanket of snow have caused consternation. Photograph: Stratis Balaskas/EPA

With resources stretched to breaking point in a nation itself dealing with economic and social crisis, the beleaguered government has appealed to other EU member states to expedite the process of taking in asylum seekers. Under an emergency relocation plan, agreed as part of the EU-Turkey deal, the 28-member bloc vowed to accept 63,302 refugees from Greece. To date only 7,280 have been relocated from the country, according to European commission data released this week.

Brawls between rival ethnic groups, attacks by far-right xenophobes, and frustration and uncertainty over what lies ahead have exacerbated tensions in camps.

In September, thousands were forced to flee Moria after members of Greece’s neo-fascist Golden Dawn party set fire to the facility.

In what it described as “an extremely urgent appeal”, the anti-racist group Keerfa said government-run installations in Athens, including a former military barracks at Malakasa, had to be closed immediately because hundreds of detainees, among them children, toddlers and disabled people were “literally freezing”.