The victims were found on a motorway near the town of Parndorf in eastern Austria.

The bodies were abandoned in the back of an Hungarian-registered truck. Hungarian authorities confirmed they believe that the driver was Romanian.

Police spokesman Helmut Marban said police stopped shortly before noon today 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.

Police chief for the province of Burgenland, where the 7.5-tonne truck was found, Hans Peter Doskozil said it was impossible to give an exact number of victims at this stage because their bodies have started to decompose.

He said: 'We can assume that it could be 20 people who died. It could also be 40, it could be 50 people.'

He said the truck, which had Hungarian licence plates but writing in Slovak, was abandoned by the people smuggling gang on Wednesday.

The state of the bodies on a hot summer day made establishing the identities and even the exact number of dead migrants difficult, and police opted to start that work once the truck was towed from the highway.

A full investigation into the tragedy has been launched, with Austrian police being joined by their colleagues in Hungary.