Leading children's charities warned Tuesday that young refugees crossing through the Balkans were at serious risk from the bitterly cold weather and lacking adequate shelter in the snowy conditions.
"It's an absolutely desperate situation," Valentina Bollenback, a spokeswoman for Save the Children, told AFP by telephone from southern Serbia near the Macedonian border, where the ground is currently covered with about six inches (15 centimetres) of snow.
She said refugees were forced to trudge through the snow for two kilometres (about 1 mile) to cross the border into Serbia. They then travel to the Presevo registration centre, where she had seen shivering children with chattering teeth and blue lips.
"There's an increasing risk of hypothermia, pneumonia, and other life-threatening illnesses," Bollenback told AFP.
While tents were being heated and local authorities were "stepping up" their efforts, she said a better system was needed to give a "dignified and humane" response to refugees.
UNICEF, the UN Children's Fund, also released a statement warning that children arriving in southeast Europe were "physically exhausted, scared, distressed and often in need of medical assistance".
"The recent sub-zero temperatures and sometimes snowy conditions (are) exacerbating the children's poor physical condition as many children on the move do not have adequate clothing, or access to age-appropriate nutrition," the statement added.
"This has been worsened by the lack of shelter and inadequate heating in some reception centres as well as buses and trains."
More than one million migrants and refugees crossed the Mediterranean Sea to Europe in 2015, nearly half of them Syrians, according to the UN refugee agency, UNHCR.
Despite the cold weather, men, women and children continue to travel from Greece across the Balkans in hope of reaching more prosperous western European countries, particularly Germany.
Mirjana Milenkovski, a spokeswoman for UNHCR in Serbia, said nearly 7,000 refugees had entered the Presevo reception centre from Friday to Monday, adding that the "situation was under control".