Large numbers of migrants and refugees are stuck in Greece as Balkan countries announce further restrictions on the number crossing their borders.
Greece is trying to slow the flow to its northern border, to prevent a build-up of people there.
Slovenia, Croatia, Serbia and Macedonia have each announced that just 580 a day will be allowed through their borders.
So far this year, 100,000 migrants have entered the EU illegally - nearly all of them arriving in Greece.
More than 400 have died on the sea crossing from Turkey.
The restrictions in the Balkans follow Austria's decision last week to introduce a daily cap.
Macedonia's Interior Minister, Oliver Spasovski, on a visit to the migrant camp in Gevgelija on the border with Greece, said his country could only accept as many refugees as the other countries on the Western Balkan route - Serbia and Croatia - would take.
Migrants held peaceful protests in Athens and at Piraeus port on Friday, angry that they are unable to leave Greece.
Hundreds have set off on foot from a transit camp near the capital, hoping to make their own way to the border.
Some carried signs reading "help us" and "we are human".
In other developments:
- German authorities say they do not know the whereabouts of 130,000 asylum seekers who were registered last year, after they did not appear at reception centres to which they had been directed
- In France, officials have been conducting tent-to-tent visits to urge residents at the "Jungle" camp in Calais to leave, following Thursday's court decision approving the government plan to clear the camp
The Greek government has asked ferry operators to reduce services bringing migrants from islands to the capital Athens in a bid to ease pressure.
The camp on the Macedonian border at Idomeni is well above capacity, and more people are waiting nearby.
Meanwhile, a row between Greece and Austria, one of the countries that has tightened its border security, has deepened, with Athens snubbing a request to visit by the Austrian interior minister.
Johanna Mikl-Leitner had warned that if Greece could not secure the external borders of the EU, then other countries would have to take action.
In northern Greece, protesters briefly blocked the entrance to a new proposed camp for migrants near Polykastro.
Some local people said they were concerned that the camp would become permanent.
The government had asked that three ships serve as temporary hotels for the refugees and migrants for two or three days, before taking them to Piraeus.
The plan particularly affects Lesbos, Chios and Samos, islands which are close to Turkey.
The Catholic humanitarian organisation Caritas tweeted that Thursday night's ferry from Lesbos had not departed, "leaving refugees and migrants stranded".
The island risked becoming "one big camp if refugees and migrants continue to arrive without any option to leave," it said.
The Athens government has been criticised by other EU countries for failing to manage the new arrivals - but no progress has been made on a European plan to relocate refugees from Greece.
Prime Minister Alexis Tsipras has threatened to block all decisions at EU migration summits next month if member states do not agree to take in quotas of migrants.
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.