Austrian police Thursday discovered the badly decomposing bodies of at least 20 – and possibly up to 50 – migrants stacked in a truck parked on the shoulder of the main highway from Budapest to Vienna. The shocking find came as Austria hosted a summit in Vienna on Europe's refugee crisis for Western Balkan nations, which have been overwhelmed this year by the tens of thousands of migrants trying to get into Europe via their territory. Police ordered reporters at the scene to move away from the vehicle, a white refrigeration truck with pictures of chicken on it. The truck, with all the bodies still inside, was later taken away to a secure location so forensic experts could examine it more thoroughly. The state of the bodies on a hot summer day made establishing the identities and even the exact number of dead migrants difficult, but the total number could rise to 50, said Hans Peter Doskozil, chief of the Burgenland police. Police spokesman Helmut Marban said police stopped shortly before noon Thursday thinking that the parked truck had some mechanical trouble. Then they "saw blood dripping" from the vehicle and "noticed the smell of dead bodies," he said. It had Hungarian license plates but the writing on its side and back was in Slovak. The state of the bodies suggested the migrants could have been dead for several days. Police said the investigation could last for days. They declined to give further information on cause(s) of death, the victims' possible identities, whether children were among them, how the migrants may have died or other details. At the Vienna migration summit Thursday, participants held a moment of silence and condemned the traffickers. "Human smugglers are criminals," Austrian Foreign Minister Johanna Mikl-Leitner said. "Those who still think that they are gentle helpers of refugees are beyond saving." German Chancellor Angela Merkel, who was also at the summit, said she was "shaken by the awful news." "This reminds us that we in Europe need to tackle the problem quickly and find solutions in the spirit of solidarity." Migrants fleeing war and poverty from the Middle East, Africa and Asia are flocking to Europe by the hundreds of thousands this year. Many follow the Balkans route, from Turkey to Greece by sea, up north to Macedonia by bus or foot, by train through Serbia and then walking the last few miles into EU member Hungary. That avoids the more dangerous Mediterranean Sea route from North Africa to Italy, where the bodies of 51 other migrants were found Wednesday in the hull of a smugglers' boat rescued off Libya's northern coast. Once inside the 28-nation EU, most migrants seek to reach richer nations such as Germany, The Netherlands, Austria or Sweden. Amnesty International alleged that EU indecisiveness was partly to blame for the latest migrant tragedy. "People dying in their dozens – whether crammed into a truck or a ship – en route to seek safety or better lives is a tragic indictment of Europe's failures to provide alternative routes," the rights group said a statement. "Europe has to step up and provide protection to more, share responsibility better and show solidarity to other countries and to those most in need."