Macedonia has allowed some migrants to board a train north overnight, as many more remain trapped on the country’s border with Greece.
Crowds of people – many refugees from the war in Syria – are continuing to build up after Macedonian authorities sealed their southern border.
Manny refugees wish to travel through Macedonia and Serbia to reach northern Europe, via Hungary.
Large numbers, including children, spent the night in the open.
According to new reports, Macedonian security forces plan to let several hundred migrants in at a time on August 22 to coincide with train departures north towards Serbia and the rest of Europe.
Migrants were beaten back with truncheons and riot shields by Macedonian security forces on August 21. Tear gas was fired.
Macedonia, formerly part of Yugoslavia, has declared a state of emergency to cope with the situation.
Meanwhile, the UN refugee agency, the UNHCR, has expressed concern for “thousands of vulnerable refugees and migrants, especially women and children, now massed on the Greek side of the border amid deteriorating conditions”.
The UNHCR urged Macedonia to “establish an orderly and protection-sensitive management of its borders” while appealing to Greece to “enhance registration and reception arrangements” on its side of the border.
It also said it had been assured by Macedonia the border “will not be closed in the future”, but did not elaborate.
Greece itself has seen almost 160,000 people landing on its shores since January, the UN estimates, with 50,000 arriving in the past month alone.
Macedonia’s Foreign Minister Nikola Poposki said all migrants had to register on entering the country and they had 72 hours to decide whether they would apply for asylum or pursue their route north.
Macedonia and its northern neighbor Serbia are not part of the European Union.
However Hungary, to the north of Serbia, is an EU member and is part of the Schengen area. This means that once in Hungary people can travel onwards throughout much of Europe (excluding Britain and Ireland) without needing to show documents at international borders.