EU and Turkish leaders are due to hold high-stakes migration talks on Monday, amid signs that efforts to stem the crisis are failing, while border fences along the migration route are creating chaos and leaving thousands stranded.
Some analysts have expressed little hope that the Brussels talks will deliver a breakthrough in the crisis, which has pitted those backing a European solution - such as Germany and Greece - against countries taking unilateral steps to stem the flows.
"I am very pessimistic," Angelo Bolaffi, Italy's leading academic on German affairs, told dpa. "I think that right now Germany is alone, with a bit of support from Italy and the desperate nation that Greece has become. The others have put up walls."
Last year, more than 1 million people reached Europe, with most of them crossing by sea from Turkey to Greece in the hope of reaching wealthy northern European countries. Many are asylum seekers fleeing the war in Syria, but economic migrants have joined their ranks.
The bloc is putting much of its hope into a deal struck with Turkey, offering to help fund the upkeep of refugees there in return for measures to prevent their departure.
But the impact has so far been limited. More than 120,000 people have already reached Europe by sea this year, according to the UN Refugee Agency.
Meanwhile, countries along the Western Balkan route are closing their gates, spurred on by an Austrian decision to impose refugee quotas. Scenes on the Greek-Macedonian border, where a fence has been erected to keep out migrants, turned ugly as clashes erupted this week.
The clampdowns have pushed Greece to the brink of a humanitarian crisis, with more than 25,000 people trapped there at present. Athens expects that this number could rise to 200,000. On Wednesday, the European Commission proposed emergency aid for Greece.
The coming days and weeks are considered by many as make-or-break for the EU's response to the crisis.
EU Migration Commissioner Dimitris Avramopoulos demanded "tangible and clear results on the ground" by next Monday, warning otherwise of a "risk that the whole system will completely break down."
"By March 7 we want a significant reduction in the number of refugees on the Turkish-Greek border," added German Interior Minister Thomas de Maiziere, at talks in Brussels last week.
Ahead of Monday's summit, EU President Donald Tusk has embarked on a whistle-stop tour of the migration route to drum up support for a common European approach.
But he has also called on Ankara for "more intensive engagement ... to avoid a humanitarian disaster," ahead of talks later this week with Turkish Prime Minister Ahmet Davutoglu and President Recep Tayyip Erdogan.
German Chancellor Angela Merkel, whose country has taken in the bulk of asylum seekers, is one of the staunchest defenders of the European approach: registering arrivals at the external EU borders; returning economic migrants; and redistributing refugees among member states.
"It is my damned duty and role that Europe finds a common way," she told German television audiences on Sunday. Merkel, whose popularity has taken a hit over her handling of the crisis, is under pressure ahead of regional elections in Germany on March 13.
Many see the migration crisis as a litmus test for the EU as a whole, at a time when euroscepticism is rife and Britain is preparing for a referendum on its future membership.
Europe will end up "losing itself" if it fails to implement what it has agreed, Italian Interior Minister Angelino Alfano warned last week, while Luxembourg Foreign Minister Jean Asselborn said the bloc was steering "into anarchy."
The crisis will remain on the agenda after Monday's summit, with new proposals to tackle the migration surge expected before EU leaders meet again in mid-March.
On Wednesday, Greek Prime Minister Alexis Tsipras appealed for solidarity. He is expected to hold separate talks with Davutoglu next Tuesday, according to Turkish media.
"Greece is the territory in which Europe will confirm its principles and basic values, such as humanism and solidarity, or betray them," Tsipras told Italian daily Corriere della Sera. "We will all succeed together, or all fail together," he added.