In November alone, almost 3,900 asylum seekers landed on Lesbos, arriving from the Turkish coast nearby.
Among them, at least 1,200 unaccompanied minors live in "extremely worrying and unsuitable" conditions for children, according to the Office of the High Commissioner for Refugees (UNHCR).
The UN agency, medical charity MSF and other NGOs have called for an emergency evacuation of children and other vulnerable migrants living in "inhuman" and "miserable" conditions, according to AFP.
"In the beginning of the winter it's really bad. It's raining everywhere. The tents can't hold it. Nothing can hold the rain. The situation is really, really bad. It's cold," says Sleem, a 22-year-old refugee from Iraq.