At least 10 people were receiving medical aid, after an attempt by Macedonian police to allow crowds of refugees to cross a busy border post at the Greek border resulted in a crush.
The border had been sealed since Thursday, after Macedonia was overwhelmed with migrants.
Reuters reported that screams were heard from the crowd, as over 1,000 people jostled in an attempt to get through. Medical personnel tried to revive those who had passed out, or were hurt in the squeeze.
Earlier, Macedonian police said they were re-opening the border, following Thursday’s emergency decree, but did not specify how many would be allowed through, possibly sparking the panic.
"We are allowing entry to a number that matches our capacity to transport them or to give them appropriate medical care and treatment," police spokesman Ivo Kotevski told Reuters.
Earlier on Friday, police fired tear gas and plastic bullets, after the migrants attempted to storm the border post. Riot police have been deployed at the checkpoint and barbed wire rolled out.
The country says it has given 181 temporary travel documents to “vulnerable” migrants in the past 24 hours, a relatively small number that is likely to result in a backlog of thousands at the border if the policy is continued for several more days.
The United Nations High Commissioner for Refugees has urged Greece to “provide urgent assistance to people on the Greek side of the border, and help them move to reception facilities away from the border.”
Commissioner Antonio Guterres said he has also personally spoken with Macedonia’s foreign minister, and "received assurances the border will not be closed in the future."
READ MORE: Macedonian police teargas thousands of refugees crossing from Greece
While Macedonia itself is not in the European Union, it has become a popular transit point for migrants streaming in from Greece. Last month, 39,000 illegal immigrants, mostly from Syria, crossed the country, twice as many as the month before.
The migrants travel through a barely-guarded border with Serbia, also not an EU member, and then into Hungary, which is part of the EU. From there, the migrants travel through the Schengen visa-free zone to Germany, Scandinavia, the UK, and other well-off northern European destinations.
Budapest has ordered a fence to be constructed along its Serbian border. This has created a last-minute rush among the illegal migrants in Greece. The UN has said that this year crisis-hit Greece has received over 160,000 migrants, through the sea routes alone, predominantly from Syria, Libya and Afghanistan.
The European Commission urged European countries to show greater co-operation in deciding where to re-settle refugees.
"We can only succeed if we work together on this, not against each other,” Annika Breidthardt, the Commission spokesperson, said in a statement.
The EU Commission has also refuted German accusations that it was not doing enough to solve the crisis.
"The proposals are all on the table. It's time that member states adopted them,” said Breidhardt.