Thousands of migrants and refugees have been stranded near Athens and on Greece’s northern border after Macedonia stopped allowing Afghans in.
Some 5,000 people were stuck on the border and another 4,000 arrived at Piraeus port, as Macedonia said only Syrians and Iraqis would be let in.
Greece has protested at the decision, but Macedonia said Afghans were not being let in by other countries.
Last week Austria imposed a daily limit of 80 asylum claims.
Although EU officials said the Austrian decision was incompatible with human rights conventions, Balkan states along the migrant route from Greece have responded by implementing their own restrictions.
In the past year, the vast majority of migrants and refugees arriving in Europe have taken the route through Greece, in the hope of claiming asylum in Germany or other EU countries. More than 1.1 million people arrived in Germany alone in 2015.
After Syrians, Afghans made up the second largest number of people seeking asylum in the EU in 2015, according to official figures.
Last November, Slovenia and other Balkan countries announced they would only allow in refugees from Syria, Iraq and Afghanistan, where armed conflicts were taking place.
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Macedonia said it was now halting access to Afghans as well, because Serbia had itself imposed restrictions, although that was disputed by the Belgrade government.
Police from Austria and the Balkan states agreed new guidelines for letting in migrants last week, which reportedly include a photo-document issued by the authorities on the Macedonian border with Greece.
The Athens government fears the new restrictions will prompt a build-up of migrants and refugees on its territory. The UN has already counted more than 94,000 arrivals from Turkey on Greece’s Aegean islands since the start of this year.
Greece’s junior immigration minister said he was hopeful the issue would soon be resolved with Macedonia but there were fears the number of stranded migrants could increase.
The first indication of that came with the arrival on Monday of four ships in the port of Piraeus carrying some 4,000 migrants from the Greek islands. They were intending to continue their journey to the Macedonian border at Idomeni.
Almost 5,000 people were already waiting either at Idomeni or on buses a short distance from the border.
German politicians have reacted with dismay to the change in Austrian policy, which includes a 3,200 daily limit on the number of migrants and refugees being allowed transit through the country.
Interior Minister Thomas de Maiziere complained the number was far too high and sent the wrong signal.
“If others think that they will dump a greater burden on Germany, we won’t accept that in the long term,” he said.
His opposite number in Austria, Johanna Mikl-Leitner, complained that Germany was sending mixed signals.
Germany could not promise Greece that it would continue pursuing its open-border policy while also demanding that Austria stop everyone coming through, she argued.
Germans have been shocked in recent days by two anti-refugee protests in the eastern state of Saxony.
Dozens of protesters blocked a bus carrying families to a shelter in the town of Clausnitz on Thursday night, hurling abuse and chanting “we are the people”.
Two nights later, a shelter for asylum-seekers was set alight in Bautzen as onlookers were filmed applauding the action.
Government spokesman Steffen Seibert condemned the Clausnitz attack as cold-hearted and deeply shameful.
A note on terminology: The BBC uses the term migrant to refer to all people on the move who have yet to complete the legal process of claiming asylum. This group includes people fleeing war-torn countries such as Syria, who are likely to be granted refugee status, as well as people who are seeking jobs and better lives, who governments are likely to rule are economic migrants.