Thousands of children, women and men are trapped on Greek islands as winter sets in without proper access to shelter, food, sanitation and healthcare, human rights groups have said, as they called on the Greek prime minister to end "the ongoing containment policy".

In a letter made public on Monday to Alexis Tsipras, 19 international and local groups including Oxfam, Human Rights Watch, Greek Forum of Refugees and Hellenic League for Human Rights decried a lack of solidarity among EU member states in taking care of refugees fleeing war and persecution.

"We urge you to put an end to the ongoing 'containment policy' of trapping asylum seekers on the islands if they arrived after the entry into force of the EU-Turkey [deal]," the groups said.

"Immediately transfer asylum seekers to the mainland and meet their protection needs, including by providing them with adequate and dignified protection, accommodation and access to services."

The EU-Turkey deal of March 2016 was designed to close the Aegean route. Most of those affected were from the Middle East and Asia.

Under the agreement, refugees arriving to the Greek islands via Turkey were to be returned to Turkey. In return, Europe agreed to accept one Syrian asylum-seeker from Turkey for every Syrian sent back there. But since the deal, Greece has merely held arriving refugees on islands.

"Some of those who arrived on the islands in the early days of the EU-Turkey [deal] have remained stuck there for 19 months," the letter said.

A recent increase in arrivals include a considerable number of women and children, the groups said.

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"The situation is particularly critical in the hotspots on Samos and Lesbos, where a total of more than 8,300 people are living in facilities intended for just 3,000."

On Lesbos, conditions are especially harsh for pregnant women and place their babies' health at risk, while some single women have reported being harassed by men.

Groups of seven people are living in summer camping tents designed for two people, the groups said, adding that wheelchair users were unable to access basic services such as water, sanitation and food.

As well as being cold, winter months can also be rainy in Greece, adding further pressure on refugees living in the open.

UNHCR, the UN's refugee agency, has also recently warned of harsh winter conditions, urging action to provide refugees with shelter and aid items.

In the winter of 2016 and early 2017, several refugees - more than five according to reports - froze to death in Europe's cold snap.

Meanwhile, the International Organization for Migration said on October 18 that at least 2,783 refugees and migrants have died while making the perilous journey to Europe across the Mediterranean so far this year.