Several arrests have been made in Hungary after the bodies of 71 refugees were found in a truck abandoned on a motorway in Austria.

Austrian police said three people had been arrested while their Hungarian counterparts said four were in detention. There was no immediate explanation for the discrepancy.

Police had originally put the death toll at between 20 and 50 after the truck was found on Thursday, but Austrian officials revised the figure upwards on Friday.

Speaking at a press conference in Eisenstadt, Austrian police official Hans Peter Doskozil said the dead comprised 59 men, 8 women and four children, including a young infant.

He said it was likely that those in the truck suffocated.

A Syrian travel document was found among the victims but more time is needed to determine whether people of other nationalities were on board, the police chief said.

Hungarian police said they had arrested four men, including three Bulgarians and an Afghan citizen, and had questioned roughly 20 people after conducting house searches.

"We expect that that this is the trace that will lead us to the perpetrators," Doskozil said, making clear that the people being held were not the ring leaders of the trafficking gang.

The truck, found on Thursday, had travelled to Austria from Hungary. The partly decomposed bodies were piled on top of each other in a cargo container in the vehicle, parked off the highway in Burgenland state.

In a separate incident, in Hungary, police said 10 Syrian refugees were injured on Friday when a van driven by a Romanian suspected of human trafficking overturned en route for Budapest.

Police in Hungary said that as of Tuesday, 776 suspected human smugglers had been detained this year, compared to 593 in all of 2014.

Over the last several days, 21 suspected human traffickers - 16 Romanians, two Syrians, two Hungarians and a Russian citizen - had been arrested and 16 vehicles carrying around 100 refugees towards the West had been confiscated, they said.

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This year has seen record numbers of people trying to reach the EU by sea and land as they flee conflicts in Africa, Asia and the Middle East.

The shocking discovery of the 71 bodies cast a shadow over talks in Vienna, where Europe's leaders had gathered on Thursday to discuss the mounting refugee crisis on the continent.

The Western Balkans conference was called to find a common European answer to the refugee crisis that is overwhelming some countries while leaving others relatively unaffected.

Austrian plan

At the summit, Austrian Foreign Minister Sebastian Kurz floated elements of a five-point plan that foresees establishing safe havens in the refugees' home countries where those seeking asylum in the EU could be processed and - if they qualify - be given safe passage to Europe.

Beyond safe havens, possibly protected by troops acting under a UN mandate, the Austrian plan to be submitted to EU decision-makers foresees increased controls on Europe's outer borders and coordinated action against human smuggling.

It also calls for refugee quotas for each of the EU's 28 members - something that many countries have opposed.

EU members Greece and Italy, and non-EU Balkan countries such as Macedonia and Serbia - whose leaders attended the summit - are dealing with the initial refugee burden through sea and land routes. But many of these refugees are only in transit to western European countries.

Nearly 300,000 people have crossed the Mediterranean this year with at least 2,373 "migrants and refugees" dying in a bid to reach Europe, nearly 300 more than the same period last year, according to the International Organization for Migration (IOM).