At least 20 migrants were found dead Thursday in a truck parked on the shoulder of an Austrian highway leading from the Hungarian border, police said.

Police official Hans Peter Doskozil said the truck, with Hungarian license plates, was found on the shoulder of the highway. He suggested the victims had been dead for some time, telling state broadcaster ORF that the bodies appeared partially decomposed.

He said the truck was apparently abandoned Wednesday and its back door was left open, exposing the bodies to police.

Doskozil, the police chief of Burgenland province, said the state of the bodies made it difficult to say how many bodies were in the truck but estimated it could be up to 50.