As some relatives visited the morgue to identify the bodies of the 28 victims, including six adults, others were driven from their hotel to the Sierre tunnel where investigators were trying to understand how the tragedy unfolded.

An AFP correspondent at the scene said the relatives could be seen clutching bouquets and messages as they boarded their coach. A young girl was among the party although it was not immediately clear whether she was a sister of one of the victims or a crash survivor.

“The visits are going on at the moment. They have been organised for the whole day on the request of the families,” a police spokesman told AFP. The tunnel remains closed to the public and the media were kept at a distance.

Meanwhile on the bridge overlooking the tunnel’s exit, residents of the region arrived to lay flowers and candles.

“I am here to lend solidarity to the victims’ families, for the other children who were on the trip, for the injured and to give support to all the rescuers who worked on this disaster,” said Elodie, a young girl who arrived clutching flowers.

After police said they did not believe the driver of the coach had been speeding, Swiss authorities acknowledged there would be a rethink about safety designs in the tunnel which stretches 2.5 kilometres.

Forty-six children and four teachers from two Belgian schools were returning home from a skiing holiday late on Tuesday when their coach slammed into a concrete wall in the motorway tunnel in southern Switzerland.

Twenty-one of the dead were from Belgium while the other seven fatalities were from the Netherlands.

Two C-130 Hercules transport planes belonging to the Belgian army were on standby to bring back the bodies of the dead, Defence Minister Pieter De Crem announced on his return from a visit to the crash site late on Wednesday.

As the parents arrived at the morgue, a police spokesman confirmed to AFP that some of the bodies would be repatriated to Belgium later in the day.

“The families are there to identify the bodies and to give information to help in the formal identification of those who cannot be identified” visually, the spokesman told AFP.

The body of the driver however was expected to remain as “health analyses have to be carried out” to check if he was suffering from an illness that could have caused the accident.

It is believed that the coach clipped a kerb and then slammed into the wall of a rectangular emergency stop area.

The Zurich daily Tages-Anzeiger said “the collision has occurred because of that wall”, noting that the design was common throughout the country.

The 100 kilometre (60-mile) per hour speed limit was also questioned by the press.

A spokesman for the federal roads service indicated the accident could lead to changes to the right-angle shape of the emergency stop areas in tunnels.

“For the moment, the emergency stop areas have this shape as called for by regulations,” said Antonello Laveglia.

“It’s clear that with what has happened, it’s not excluded that something will be re-discussed or changed,” he said. “The accident is an occasion to think further on this topic.”

The coach had only just reached the motorway after a short descent along winding roads from the mountain ski resort, close to the Italian border.

Marianne Van Malderen, a Belgian motorist who arrived at the scene shortly after the crash, described children pinned under their seats or thrown towards the front of the coach.

“We did what we could to get out those who were unhurt,” but “it wasn’t possible to climb into the coach because its windows were so high up”, she said. 

While Switzerland pondered how the tragedy had occurred, the overwhelming emotion in Belgium was grief.

“Belgium Weeps for its Children,” read the headline in the French-language newspaper la Derniere Heure, while newspaper Le Soir run a dark front page with a picture of the tunnel and a headline “State of Shock.”

Newspapers in the Flemish region of Belgium, home to the two Catholic schools that the 11- and 12-year-old children attended, dedicated dozens of pages to the tragedy.

The daily De Morgen said: “There is no satisfactory answer to this question: why my child?”

Belgium’s Prime Minister Elio Di Rupo said he could find no words of comfort for devastated relatives.

“When we lose an adult it’s dramatic, when we lose a child there are no words… because the pain is so great that there is nothing to relieve the pain,” Di Rupo told a press conference in Sion late Wednesday.