European Union and Balkan leaders are holding emergency talks on Europe's refugee crisis amid threats from three front-line states to close their borders if northern EU countries stop accepting refugees.
The summit on Sunday, called by European Commission President Jean-Claude Juncker, groups the heads of 10 EU nations, including German Chancellor Angela Merkel, in addition to the leaders of Albania, Serbia and Macedonia.
The meeting came after Bulgaria, Romania and Serbia on Saturday warned they would not allow themselves to become a "buffer zone" for the tens of thousands of arrivals streaming into Europe.
"All three countries ... are ready if Germany and Austria and other countries close their borders [...], we will be ready to also close our borders at that very same moment," Bulgarian Prime Minister Boyko Borisov said after talks between the three Balkan leaders in Sofia.
Over the past months, non-EU member Serbia has seen a massive influx of refugees on their way from Greece and Macedonia to northern Europe, though Bulgaria and Romania have been much less affected.
Juncker's office said Sunday's small summit was needed to foster greater cooperation "in view of the unfolding emergency".
In an interview published on Sunday by the German newspaper Bild, Juncker urged countries to stop handing over refugees to neighbouring states in chaotic conditions.
States "must take care to uphold orderly procedures and conditions", he said.
"The European Commission expects everyone to obey the rules of the game if we don't want to put Schengen at risk," Juncker said, referring to the EU's border-free zone.
The EU is facing record arrivals with more than 47,500 people in the last week entering Slovenia, which has a population of just two million, and 48,000 entering Greece, which has a population of 11 million, according to official figures.
Warning of humanitarian disaster
With winter looming, Amnesty International on Saturday warned of a humanitarian disaster if refugees are stranded at borders.
"Every day counts," Juncker told Bild. Without action, "we will soon witness families dying wretchedly in chilly rivers in the Balkans".
Slovenia is seeking help after becoming the main entry point into the Schengen zone when Hungary sealed its southern borders with coils of razor wire.
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Slovenia has asked Brussels for $155m in addition to police backup and logistical support to deal with its refugee influx. It says that if no help emerges, it may have to build its own border barrier with Croatia.
Meanwhile, at least three refugees - a woman and two children - drowned on Sunday when their boat sank off the Greek island of Lesbos, the country's coastguard said after discovering their bodies.
About a dozen others, mostly from Afghanistan, are still missing after the rickety vessel carrying 60 people sank at dawn as it made the perilous crossing from Turkey.