The Macedonian authorities shut the border with Greece on Saturday. Some 4,000 people are currently in temporary camps in Greece, according to the media outlet.
Earlier in the week, Croatia implemented a set of measures to prevent undocumented migrants from entering the country with the aim of traveling onward to other European states, such as Austria and Slovenia. Zagreb's move led to an accumulation of migrants within Serbia.
Europe has faced an enormous influx of migrants fleeing war and poverty in the Middle East and Africa. Many refugees use transit routes through the Balkans to reach more prosperous countries in Western Europe.
EU border agency Frontex recorded over 1.83 million illegal border crossings into the European Union in 2015.