Police in Austria say it may tale until tomorrow to count the number of people found dead in a lorry on a roadside in the country.

It's understood at least 50 refugees suffocated to death in the vehicle.

The refridgerated vehicle was discovered on the hard shoulder of the A4 highway, close to Parndorf, about 50 km southeast of the capital Vienna and about 25km from the Hungarian and Slovak borders, according to Krone newspaper.

It is thought they were trapped in the trailer and suffocated after being unable to get out - but police said it was too early to confirm the cause of death.

The van had been seen stationary by staff at a nearby service station and when it failed to move for some time, they called the police.

One witness said that liquid was seen leaking out of the back of the chilled foods lorry. The driver is believed to have fled the scene and is currently being sought by police.

At a press conference in Eisenstadt, Interior Minister Johanna Mikl-Leitner said it demonstrated "the despicable methods used by Mafia traffickers in all their ugliness in Austria".

"Today is a dark day," she said vowing there would be zero tolerance shown towards any that were caught.

Ms Mikl-Leitner said: "These people belong behind bars! These Mafia traffickers must know that they cannot feel safe in Austria".

The interior ministry confirmed there had been between 20 and 50 deaths.

Earlier, three other vehicles were seized in Bruck an der Leitha, a short distance further northwest, one of which contained 34 refugees.

That group had been saved but had complained about being almost unable to breathe once inside the back, Krone said.

It was alleged that the driver had ignored multiple requests to stop on their journey from the Serbian border to Austria.

It came as thousands of migrants and refugees a day are being travelling between Greece to Hungary as they seek a better life in the European Union.

They are taking the perilous "Balkan Corridor", with many of the countries on the way feeling the strain of so many people passing through.

The news came as the European Union held a summit in Vienna to discuss the refugee crisis.

Speaking in Vienna, German Chancellor Angela Merkel said she was "shaken" by the tragedy.

And EU Commission Foreign Affairs chief, Federica Mogherini, is calling on member states to do more to prevent such tragedies.