Migrant families have been warned of the cold in Serbia, with temperatures set to drop to -20C (-4F) on the Macedonia border. An estimated 1,000 refugees still cross there each day, and on Tuesday 19 January Save the Children warned that some people were arriving at reception centres with "blue lips and shaking from the cold".

An unnamed Syrian father of three said: "I didn't have to think much about weather in Syria. The children are having a harder time with it. And to come all the way from Syria, it's a long distance."

He added: "The journey is difficult. We're all extremely tired. The weather here is bad, but what can you do? We're not too tired, because we're hopeful. We've travelled by boat, we've travelled by bus. We're not too tired to continue."

Aid workers in Belgrade have also warned that they have found some possible cases of hypothermia and frostbite in children travelling from Syria. One border centre at Presevo has seen families arriving throughout the day and night, with snow and ice on the roads.

More than one million people travelled across the Mediterranean in 2015 seeking sanctuary in Europe according to the United Nations' refugee agency. It is thought around 3,700 people have died so far due to the perilous conditions.