Balkan countries are threatening to close their borders if European Union members in northern Europe stop accepting asylum seekers streaming north from Greece and Macedonia.
The mini-summit called by European Commission president Jean-Claude Juncker, groups the heads of 10 EU nations including German chancellor Angela Merkel, plus the leaders of Albania, Serbia and Macedonia.
Bulgaria, Romania and Serbia 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 past months, non-EU member Serbia has been swamped by asylum seekers on their way to northern Europe, though Bulgaria and Romania have been much less affected.