Police discovered the decomposing bodies of between 20 to 50 migrants stacked in a truck parked on a highway in Austria.

The grisly discovery came as Austria hosted a summit in Vienna on Europe's refugee crisis for Western Balkan nations and Germany, which has been overwhelmed this year by a massive influx of migrants trying to enter Europe through its territory, according to the Los Angeles Times.

"Today is a dark day... This tragedy affects us all deeply," said Interior Minister Johanna Mikl-Leitner during a press conference.

The truck, bearing Hungarian license plates, was found in an emergency lane off the highway near the Hungarian border, police spokesman Hans Peter Doskozil said alongside the minister, reported AFP. The writing on the truck's exterior was in Slovak.

Initial reports indicated the truck had been parked in the area since Wednesday with the back door left open, according to the Times Of Israel.  

Hungary said the dead appeared to be victims of a human trafficking operation and that it would aid Austria in the investigation.

Police noted the investigation could go on for days. Due to the state of the bodies, they were unable to immediately provide information about who the victims were or if there were any children among them. "We cannot confirm yet how they died," said Doskozil.

Mikl-Leitner condemned the actions of the alleged smuggler saying, "Human traffickers are criminals. Anyone still thinking that they're kind helpers cannot be helped."

"These people belong behind bars," she concluded.