The bodies of up to 50 migrants have been found in a truck on a highway in Austria, the latest tragedy involving people desperately trying to reach Europe.

"Today is a dark day," Interior Minister Johanna Mikl-Leitner said at a press conference on Thursday.

"This tragedy affects us all deeply."

The vehicle, bearing Hungarian number plates, was found in an emergency lane off the highway near the border with Hungary, police spokesman Hans Peter Doskozil said alongside the minister.

Hungary said the dead appeared to be victims of a people-trafficking operation and that it would join the Austrian investigation into the tragedy.

A spokesman for Hungarian Prime Minister Viktor Orban said the driver was Romanian.
It is thought the truck - bearing the markings of Slovakian poultry firm Hyza - had been parked in the area since Wednesday.

"Human traffickers are criminals," the minister said. "Anyone still thinking that they're kind helpers cannot be helped."

Forensics teams at the scene said it would take several days to secure evidence.

"We cannot confirm yet how they died," Doskozil added.

Mikl-Leitner announced Austria would tighten its border controls and intensify checks on international trains in the coming weeks.

She also called on the other 27 member states of the European Union to show "zero tolerance" for people smugglers.

The gruesome find comes as German Chancellor Angela Merkel and Balkan leaders were meeting in Vienna to discuss how to tackle together the biggest migration crisis to hit Europe since World War II.

The Austrian tragedy comes after at least 55 dead bodies were discovered Wednesday on three overcrowded migrant boats in the Mediterranean.

More than 2300 migrants have died at sea this year during attempts to reach Europe, almost invariably on overcrowded boats chartered by people smugglers.