The UN refugee agency has called for the urgent evacuation of families and sick people from the Moria camp on Lesbos. Over the weekend boats continued to arrive on the Agean islands, sending more families into “alarming” and overcrowded conditions in the refugee camps.

The Moria camp in Lesbos has grown from a population of 5,000 last July to around 20,000, with new families arriving daily. Even the most vulnerable new arrivals can no longer find space in the official area, but have to build makeshift shelters in a rubbish-filled olive grove around the camp.

Over 85% of arrivals last year were refugees. The majority of families came from Afghanistan and Syria, but also from Iraq, Palestine, Somalia, the DRC, and elsewhere.

UNHCR spokesperson Andrej Mahecic said: “More than 36,000 asylum seekers are now staying in reception centres across five islands which were originally designed for 5,400 people. We are seriously concerned about the limited access to health services at the reception centres which is aggravated by the difficult living conditions.

“Greece has been generous and compassionate towards refugees, despite a very complex and difficult situation, and the East Aegean islands have taken on a vastly disproportionate burden and responsibility. It is critical that other regions in Greece step up their solidarity to help alleviate pressures by receiving transferred asylum seekers and opening up reception places.

“There is an urgent need for the government to speed up the implementation of its plans to move thousands of asylum seekers from the islands to the mainland.”

More than 42,000 men, women and children are estimated to be on Lesbos, Samos, Chios, Leros and Kos. Unable to leave because of a containment policy determined by the EU, they are forced to remain on the islands until their asylum requests are processed by a system both understaffed and overstretched.

Doctors say it is impossible to heal patients in the current conditions. Photograph: Aris Messinis/AFP via Getty Images

Dr Hana Pospisilova is a consultant cardiologist who regularly volunteers on Lesbos. She told the Guardian that she has serious concerns that the failure to treat very sick and vulnerable individuals could lead to a major public health crisis.

“I am an experienced doctor, I have seen many patients in my life, but what I saw there had me crying. I saw many children I was worried would die because they were suffering malnutrition. I met a baby who smelled bad; his mother had not washed him for weeks because there was only cold water and she was worried he would die.

“There are children, between 12 and 15, living in the olive grove and they are barefoot. A lot of them have scabies and we can’t treat it because they have to wash. But they say to wash means waiting three hours and it’s risky: people have knives, and you can only have two minutes in the shower after you wait.

“I tell them they need to discard their clothes and they say ‘I have only these clothes.’ They have had them on for seven months. I saw everyday 20 people and all 20 had a horror story.”

Her main concern is that the dire conditions could lead to a pandemic.

“ I saw many people with respiratory problems and even though it’s cold, it’s winter, we are sending these people back to wet tents in an overcrowded camp. I am worried about a pandemic breaking out. They don’t have hot water, they have to wait three hours in the cold for food, they aren’t getting enough vitamins so many have bleeding gums.

“People come and go to the medical facilities, they take antibiotics, they are still coughing, they still have a temperature. If you read about Spanish flu it was exactly like this that is began to spread, in overcrowded facilities where people had a viral infection that became a bacterial infection that killed them.

“This is what makes me worried. We are treating patients but nobody is healed, it’s impossible to heal them in these conditions.”

Doctors currently on the island have been warning that conditions are so bad lives are being put at risk on a daily basis.

The UN also warned that since July last year asylum seekers have no longer been issued with the unique number which grants them access, free of charge, to the state healthcare system. As a result, outside of emergency support, asylum seekers – including those with chronic conditions – are unable to access state-provided treatment and medication.

Last week the region’s most senior official likened the situation on Lesbos to a “powder keg ready to explode”. Kostas Moutzouris, governor of the north Aegean, said: “It’s crucial that a state of emergency is called.”

• The headline on this article was amended on 11 February 2020 to remove a reference that wrongly linked the UN to fears of a pandemic breaking out in the camp.