EU interior ministers pushed Thursday for a coordinated approach to the continent's migration crisis, with Luxembourg's Foreign Minister Jean Asselborn warning that the bloc was heading towards "anarchy."
Europe has been struggling to deal with a surge in migration that saw more than 1 million people arrive in 2015. Many are asylum seekers fleeing the war in Syria, but economic migrants have also joined their ranks.
The short sea passage from Turkey to Greece has been the main crossing point to Europe.
The European Union has responded with initiatives aimed at securing Greece's borders and registering arrivals, improving cooperation with Turkey and internally redistributing asylum seekers that have reached European shores.
But implementation is lagging, prompting several countries along the migration route to northern Europe to take unilateral measures, limiting access for migrants and asylum seekers.
The move has led to a backlog of people in Greece and warnings that the country could slide into a humanitarian crisis. Prime Minister Alexis Tsipras has threatened to block EU decision-making processes if the situation does not improve.
"Greece will not accept unilateral actions. Greece, too, can take unilateral action," Ioannis Mouzalas, the Greek minister in charge of migration, said Thursday. "Greece will not accept becoming ... a warehouse of souls," he added.
On Thursday, hundreds of desperate migrants stranded in Greece began marching toward the border with Macedonia.
TV reports showed women carrying children as they walked through the Tempi gorge on the highway from Athens towards Idomeni on the border, 200 kilometres to the north.
"We have no [common] line any more, we are steering somehow into anarchy," Asselborn said in Brussels, ahead of the meeting with his 27 EU counterparts.
Turkish Deputy Interior Minister Sebhattin Ozturk was also due to join the talks, as well as UN High Commissioner for Refugees Filippo Grandi and representatives from countries along the Western Balkan migration route.
"We really have to pull ourselves together before it is too late," Asselborn added, warning that European citizens were losing trust in their leaders to resolve the problem.
"If Europe is not able to implement what it has agreed, it is a Europe that will end up losing itself," added Italian Interior Minister Angelino Alfano.
The ministers were due to discuss a proposal giving the EU greater powers to secure the bloc's external borders, but no decisions are expected. The plan would allow for EU action if a country is unable to protect its borders - a move resisted by some.
Hours ahead of the Brussels meeting, the NATO military alliance finalized plans for an operation in the Aegean Sea to monitor migrant smuggling operations.
The aim is to feed information to the national authorities in Greece and Turkey, in cooperation with EU border agency Frontex, to help crack down on human trafficking and criminal networks fuelling the migration crisis.
"NATO's task is not to turn back the boats," said NATO Secretary General Jens Stoltenberg, while adding that its vessels were bound by the international duty to rescue people in distress at sea.
"In case of rescue of persons coming via Turkey, they will be taken back to Turkey," Stoltenberg added.
NATO sources said the operation is expected to deliver first results by March 7, when the EU is holding an extraordinary migration summit with Turkey.
Both Turkey and Greece are NATO members, while only Greece is in the EU.
In Greece meanwhile, more migrants massed on the mainland Thursday, with at least 2,350 expected to arrive by ferry from Aegean islands.
More than 100,000 people reached Greece from Turkey since the start of the year, according to the International Organization for Migration.
Border restrictions implemented by Macedonia and other countries on the Balkan migration corridors have led to a notable reduction in the northward flows.
On Wednesday, Macedonian police allowed 574 people to enter - 589 Syrians and 85 Iraqis. The country has stopped allowing Afghans to pass, after an overall 26,546 crossed the country towards Serbia in the first seven weeks of the year. Only Syrians were more numerous.
Croatian police said they registered just 507 migrants on Monday, Tuesday and Wednesday, and Slovenia only 478 - compared to an average of 1,900 daily before Macedonia tightened its border.