Belgium is sending military planes to Switzerland to pick up the bodies of the 22 students and six adults killed during a bus crash in the Swiss Alps on Tuesday night.

The children, mostly from the Flanders region of Belgium, were on their way back home from a ski vacation when the accident occurred in the town of Sierre in the Swiss state of Valais.

Authorities have been unable to piece together the cause of the accident. According to Swiss police, the bus was traveling at the speed limit and those on board -- namely children from two Belgian schools -- were wearing their seat belts when it slammed into the side of a highway tunnel.

The impact of the crash completely shredded the front of the modern bus, according to reports, and trapped passengers inside.

While the driver was thought to be well rested and safely piloting the vehicle, Olivier Elsig, a prosecutor for Valais, believes that the accident could only have been caused by a health problem with the driver, human error or a technical problem with the bus, according to the Associated Press. Video cameras in the tunnel caught the accident.

We found an apocalyptic situation when we arrived, Valais police commander Christian Varone told reporters at the scene.

The screams of children were the first thing we heard, rescuer Alain Rittiner told Swiss television, describing the scene as worse than anything you can imagine.

Access to the vehicle... was difficult and it was hard to remove the victims. Emotions ran high, and with so many children, it was an absolute horror, he said, adding that the sight momentarily stunned the emergency workers.

A 200-person strong search-and-rescue crew worked through the night. The rescuers pulled 24 student from the wreckage alive, all injured, who have been taken to a hospital and are expected to return home soon.

On Thursday, family members of the victims were flown to the crash site, where they were asked to identify the bodies.

Belgium called a day of mourning, and local memorial services were held in Flanders. The United Swiss Federal Assembly paused for a moment of silence before a parliamentary debate on Wednesday.

“Switzerland will do everything it can to support the families,” Swiss President Eveline Widmer-Schlumpf said at a press conference.