Police in Austria say the bodies of 71 people, thought to be migrants, were found in an abandoned lorry found on a motorway on Thursday.
The bodies of 59 men, 8 women and four children are thought to have been dead for one-and-a-half to two days.
Police said the victims appeared to be migrants from Syria and probably died after suffocating in the vehicle.
Three people, thought to be Bulgarian, have been detained in Hungary. They are believed to have driven the lorry.
Police sent to investigate the dumped lorry on the A4 road towards Vienna discovered the decomposing bodies on Thursday morning.
The victims were probably already dead when the vehicle crossed into Austria from Hungary, authorities said.
The vehicle was towed to a customs building with refrigeration facilities in Nickelsdorf where forensic teams worked through the night to examine the bodies.
The vehicle bears the logo of a Slovakian poultry company, Hyza, which said it no longer owned the vehicle - but the buyers had not removed the branding.
The Hungarian prime minister's chief of staff, Janos Lazar, said on Friday that the lorry was registered to a Romanian citizen in Kecskemet, a city in central Hungary.
Hans Peter Doskozil, police chief in the Burgenland province where the lorry was found, said it was a refrigerated vehicle - not the typical choice for people smugglers, he added.
The lorry, which has Hungarian number plates, is understood to have left Budapest on Wednesday morning.
Tens of thousands of migrants from conflict-hit states in the Middle East and Africa have been trying to make their way to Europe in recent months.
A record number of 107,500 migrants crossed the EU's borders last month.
Some of them pay large sums of money to people smugglers to get them through borders illegally.
Meanwhile, migrants continue to die as they try to reach Europe via the central Mediterranean route.
Hundreds of people are feared to have died after two vessels carrying migrants sank off the coast of Libya on Thursday.
(BBC)
