Up to 50 refugees have been found dead in a truck in Austria, as German Chancellor Angela Merkel and Balkan leaders gathered in Vienna to decide on how to collectively tackle the biggest refugee crisis to hit Europe since World War II.

The vehicle, which contained between 20 and 50 bodies, was found on a parking strip off the highway in Burgenland state, police spokesman Hans Peter Doskozil said at a Thursday press conference with Interior Minister Johanna Mikl-Leitner.

"This tragedy affects us all deeply," Mikl-Leitner said. "Human traffickers are criminals. Anyone still thinking that they're kind helpers cannot be helped."

It was not immediately clear how the people in the truck had died, since bodies had begun to decompose.

"We can assume that it could be 20 people who died. It could also be 40, it could be 50 people," the police chief said.

He said "many things" indicated the refugees were already dead when they crossed the border.

The refrigerated truck, which had Hungarian number plates, had apparently been standing off the highway since Wednesday.

A Hungarian government official said a Romanian citizen had registered the number plate in the eastern Hungarian town of Kecskemet.

More than 28,300 people applied for refugee protection in Austria in the first half of the year, with many coming from Syria.

'Must take responsibility'

"The refugees who died today wanted to save their own lives by fleeing, but instead lost their lives at the hands of traffickers," Austrian Chancellor Werner Faymann told the summit in Vienna.

"It shows once again how necessary it is to save human lives by fighting criminal traffickers. It shows that we must take responsibility and give asylum to those people who are fleeing."

The German chancellor said everyone at the summit had been "shaken" by "appalling" news of the bodies found.

"This reminds us that we must tackle quickly the issue of immigration and in a European spirit - that means in a spirit of solidarity - and to find solutions," Merkel said.

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The talks came amid growing criticism of the European Union's failure to agree on a joint response to the unfolding crisis.

Countries taking part include Macedonia and Serbia, two major transit nations for the thousands of migrants and refugees trying to enter the EU by taking the so-called "western Balkans route".



The foreign ministers of both countries called for a concerted EU action plan at the start of the summit.



"Unless we have a European answer to this crisis ... no one should be under any illusion that this will be solved," Macedonia's Nikola Poposki said.

Meanwhile, EU member state Hungary, which is a member of the EU's passport-free Schengen zone and has become the bloc's main entry point for refugees arriving by land along the Balkans route, was not at the meeting.

The daily number of people crossing into Hungary hit a new high on Wednesday, topping 3,000, including nearly 700 children, police figures showed. Hungarian lawmakers will debate next week whether to deploy troops to stem the influx.

'Prove compession'

Alarmed by the growing humanitarian disaster, United Nations 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 meanwhile have called for the urgent creation of more so-called "hotspots" - processing centres to sort refugees fleeing war, from economic migrants simply in search of a better life.

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Nearly 300,000 people have crossed the Mediterranean this year with 2,373 migrants and refugees dying in a bid to reach Europe, nearly 300 more than the same period last year, according to the International Organization for Migration (IOM).