The 71 people found dead in an abandoned refrigeration lorry in Austria had been crammed in, five to a square metre (10 sq ft), police said on Sunday, as initial forensic tests indicated they had suffocated.

A baby girl and three other children were among the dead in truck discovered on Thursday on a highway from the Hungarian border to Vienna, where it had been left 24 hours earlier.

The victims are thought to be refugees from Syria or possibly Afghanistan, part of an huge wave of migrants pushing through Europe that is sorely testing the European Union’s ability to cope.

Forensic examiners in Vienna have performed autopsies on 16 of the 71 bodies, said Gerald Pangl, police spokesman in the province of Burgenland where the truck was found.

“We are still awaiting the final report from the forensic team, but it looks like they suffocated.”

Police said the vehicle, designed for the transportation of meat products, had no air holes. Technical specialists were still trying to establish whether a cooling unit was operational and had been running at the time of the transport, Pangl said.

Hungarian police said on Sunday they had arrested a fifth suspect, a Bulgarian citizen, in connection with the deaths and under suspicion of human trafficking. Three Bulgarians and one Afghan had already been arrested.

In another incident, two one-year-old babies and a five-year-old child who were found critically ill in the back of a van in Austria on Friday together with 23 other refugees from Syria, Afghanistan and Bangladesh have recovered and left hospital, authorities said.

Uwe Wintergerst, head doctor of the paediatric department in Braunau, a town close to the German border near to where the van was stopped, said the children had been travelling for 20 days.

“As a result of a lack of food and drink, they were dehydrated and so we took them in, gave them liquids intravenously,” he said. “They were stable enough to be able to make the decision to leave the hospital.”

Police said they were unsure of the whereabouts of the two families, but that they had wanted to go to Germany. The Romanian driver of the van was arrested.

Austrian police said they had arrested five men in four separate cases over the past two days in the region bordering Hungary for smuggling a total of 36 people. (Additional reporting by Marton Dunai in Budapest, Robin Raimund in Braunau and Shadia Nasrallah in Vienna; Editing by Raissa Kasolowsky and Robin Pomeroy)