The bodies of more than 70 people, thought to be migrants, have been found in an abandoned truck found on an Austrian highway on August 27, Austrian authorities say.
Authorities originally estimated that between 20 to 50 people died in the vehicle, found near the Hungarian border.
Police sent to investigate the dumped truck on the A4 road towards Vienna discovered the decomposing bodies.
The local police chief said it appeared those in the truck had been dead for one-and-a-half to two days.
The vehicle was towed to a customs building with refrigeration facilities in Nickelsdorf where forensic teams worked through the night to examine the bodies.
Austrian police are expected to reveal the exact toll at a news conference at 11:00 on August 28.
The police forces in Austria and Hungary are working together to try and find the driver.
A report in Austrian newspaper Krone said on August 28 that seven people had been arrested in Hungary, but this has not been confirmed.
The truck 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 August 28 that the truck 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 truck, which has Hungarian number plates, is understood to have left Budapest on August 26.