[VIENNA] Austrian police found the decomposing bodies of up to 50 migrants in an abandoned truck on Thursday, sparking a cross-border hunt for the people-smugglers responsible in the latest tragedy in the Europe-wide crisis.
The grisly discovery on a motorway near the Slovakia and Hungary borders came as European leaders again met to try to find ways to handle the flow of tens of thousands of people seeking refuge in the European Union.
Police said the vehicle - which had the markings of a Slovakian poultry company and Hungarian number plates - contained between 20 and 50 bodies.
German Chancellor Angela Merkel, in Austria for a summit with Balkan leaders, said she was "shaken" by the "horrible" news.
"This is a warning to us to tackle this migrants issue quickly and in a European spirit, which means in a spirit of solidarity, and to find solutions," Ms Merkel said.
This year over 2,300 men, women and children have drowned in the Mediterranean after rickety boats operated by people-smugglers capsized, but the latest tragedy brought home how dangerous the land journey is too.
"Today is a dark day... This tragedy affects us all deeply," Interior Minister Johanna Mikl-Leitner told a press conference.
"Human traffickers are criminals. Anyone still thinking that they're kind helpers cannot be helped," the minister said.
Police said more details including the number of dead would be given on Friday morning. The lorry, which police said was leaking "decomposing body fluids", was taken elsewhere for the bodies to be removed.
Hungary, which has received more than 100,000 migrants this year including a record 3,000 on Wednesday alone, said it would join the Austrian investigation.
"The tragic event shows how the EU's migration policy has failed," Hungary's ruling party Fidesz said.
"Instead of the current unregulated border-crossing, controlled border-crossing and border defence is needed to avoid such cases happening."
European leaders have come under fire for failing to tackle the arrival of several hundred thousand migrants this year, many fleeing hotspots such as Syria, Iraq and Afghanistan.
The western Balkans has become a major route for migrants and refugees trying to cross over into EU member state Hungary. Most then try to make it to wealthier European countries like Germany and Sweden.
Speaking at the Vienna meeting, Serbia's Foreign Minister Ivica Dacic said outside money provided so far was insufficient to handle the large numbers.
"I have to be very direct here. Please understand, we are bearing the brunt of the problem," Mr Dacic said.
This was echoed by his counterpart from Macedonia, which last week declared a state of emergency and shut its border with Greece for three days after being unable to cope.
"Unless we have a European answer to this issue, none of us should be under any illusion that this will be solved," Nikola Poposki said.
Reiterating his call for a reform of the Dublin Accords "to distribute refugees fairly within the EU", Germany's Foreign Minister Frank Steinmeier said Berlin would contribute one million euros (S$1.54 million) to help.
But with large numbers of people from the western Balkans among the migrants, he also called on governments there to make clear to their citizens that their chances of obtaining asylum in Germany are "virtually non-existent".
Alarmed by the growing humanitarian disaster, UN chief Ban Ki-moon has urged countries "in Europe and elsewhere to prove their compassion and do much more to bring an end to the crisis".
UN refugee chief Antonio Guterres and French Interior Minister Bernard Cazeneuve called for the urgent creation of more so-called "hotspots" - processing centres to sort refugees fleeing war from economic migrants who are simply in search of a better life.
Hamstrung by a lack of a coherent European response, governments have at times taken contradictory approaches to the problem.
While Hungary's right-wing government is building a 175-kilometre (110-mile) razor-wire barrier to keep migrants out, a Czech minister has called for the passport-free Schengen zone to be closed with the help of NATO troops.
Romania also said Thursday that the authorities would "as a precautionary measure" reinforce security at its border with Serbia. Romania is in the EU but not in Schengen.
Meanwhile Germany, which is preparing to receive a record 800,000 asylum-seekers this year, has eased the application procedure for Syrians fleeing the brutal civil war.
But Berlin's largesse has not been welcomed by everyone at home, particularly in the east where a spate of attacks has targeted refugee centres.
On a visit to a migrant shelter in the eastern town of Heidenau, Ms Merkel was greeted by about 200 protesters, some booing and shouting "traitor, traitor" and "we are the mob".
However, the German leader vowed: "There will be no tolerance of those who question the dignity of other people."