The United Nations on Friday urged Greek authorities to accelerate winter preparations in the refugee sites on the islands.
The UN Refugee Agency (UNHCR) said in a statement that many refugees in the state-run camps were living "in small tents and shelters unsuitable for the winter".
The agency said Greek authorities should ensure adequate shelters and distribute winter aid items as "conditions are quickly deteriorating amid increased arrivals while harsh, rainy and cold weather is expected".
"Last year, snow and freezing temperatures caused suffering for people in unheated shelters," the UN noted.
The UN added sea arrivals to Greece this year "have reached 20,000 and the majority were Syrian or Iraqi".
