The food delivery truck was found parked on the shoulder of the A4 highway near the town of Parndorf, according to an interior ministry spokesperson.
“Unfortunately there are many dead people in there,” the spokesperson said. He described the people as refugees, but said he did not have an exact number of those found in the lorry.
Meanwhile, Austrian police say the number of those dead could range from 20 to 50.
“The level of information is currently very poor. One can imagine how the condition of these people is. Therefore we can not yet say how many dead there are also,” National Police Director Hanspeter Doskozil said.
A “massive” police manhunt has been launched to locate the lorry driver, according to Krone.
Police received an alert about the vehicle around 11:30 a.m. local time on Thursday. When officers arrived at the scene, they discovered putrefaction liquid at the rear of the truck.
Interior Minister Johanna Mikl-Leitner said during a press conference in Eisenstadt that “today is a dark day.”
She spoke of the “despicable methods” of migrant smugglers, saying they “belong behind bars.”
Earlier on Thursday, Austrian police said they had stopped three vehicles suspected of carrying refugees. Included in that number was a van which had taken 34 migrants, including 10 children, into the country.
It comes amid a worsening migrant crisis in Europe, with tens of thousands of refugees from the Middle East and Africa – primarily Syria – trying to make their way to Europe’s borderless Schengen zone.
More than 28,300 people applied for refugee protection in Austria in the first half of 2015.