Macedonian riot police have used tear gas and stun grenades to disperse thousands of migrants and refugees trying to cross the border from Greece.
Thousands of people -- mainly from Syria, Afghanistan, and northern Africa -- spent the night in an area between the Macedonian-Greek border near the town of Gevgelija after Macedonia declared a state of emergency on its borders and brought in soldiers to stem an influx of migrants wanting to go north to EU countries.
The migrants tried several times to storm Macedonian police after the border was closed. At least four people were reported injured.
Macedonia's Interior Ministry declared the state of emergency on August 20 after what it called an overwhelming flow of migrants had entered the country in recent weeks -- part of a crisis that has posed an increasing challenge for Europe in recent months.
"Due to increasing pressure on the southern border...it is estimated that greater and more efficient control is needed in the region where illegal border crossings from the Greek side have been massively registered," a government statement said.
By law, declaring a state of emergency allows for the "appropriate engagement of the army" -- a move the government said it expected would "increase security of the local population" and improve the handling of migrants.
Macedonia, which is not in the European Union, is a major transit country for migrants from the Middle East, Africa, and Asia who enter the EU in Greece and try to travel northward to prosperous member-states such as Germany and Scandinavian countries.
Macedonia had previously sent riot police to impose order in Gevgelija, which has seen thousands of refugees arrive in recent days. Police have been ordered to stop the large crowds from making their way on foot to the railway station in the town, where migrants frequently board trains bound for Serbia.
At the same time, a main railway linking the Greek port city of Thessaloniki and the Macedonian capital, Skopje, was blocked by thousands of migrants. Two cargo trains and a passenger train were halted on the Greek side of the border on August 20.
PHOTO GALLERY: Migrants Stranded At Macedonian Border
Migrants who make it to Gevgelija register at the local police office and are given 72-hour permits that allow them to cross Macedonia. At the station they board special trains that take them to the village of Tabanovce on the border with Serbia -- from which many seek to enter EU member Hungary.
Nongovernmental and humanitarian organizations, which pressured the government to bring about legislative changes enacted in June to allow migrants safe passage through Macedonia, say that shutting the border would allow for the illegal smuggling business to thrive once again.
Macedonian authorities on August 19 asked for neighboring countries to send railway cars, but the UN refugee agency urged the government to do more, saying it should allocate a site to properly accommodate the 1,500-2,000 migrants and refugees now arriving daily, up from 200 per day in May.
Almost 39,000 migrants, most of them from Syria and Afghanistan, have been registered to pass through Macedonia in the past month. More could arrive, as thousands were being evacuated from the Greek island of Kos to the mainland after 21,000 people landed on Greek shores last week alone.
A passenger ship that has acted as accommodation and registration center for Syrian refugees since August 16 was expected to dock in Thessaloniki on August 20.
If the migrants aboard are allowed to disembark, they are likely to head for Gevgelija.
In Serbia, conservative Prime Minister Aleksandar Vucic said authorities would open a temporary shelter in the capital, Belgrade, to house migrants and refugees currently camping in a park outside the main railway station, before they continue north to Hungary.
Hungary is building a fence to keep migrants out, angering Belgrade.
With reporting by Reuters, AFP, and AP