Updated at 3:21 a.m. ET
(CBS/AP) GENEVA - A tourist bus crashed head-on into a concrete wall in a Swiss Alps tunnel, killing 28 people, mostly children returning from a ski vacation. Swiss police said Wednesday it was not speeding at the time.
22 school children and six adults including the driver were killed late Tuesday as they returned to Belgium from the Alps, police said. The crash, which sent another 24 children to the hospital, left the front of the bus mangled, trapping some people inside.
Another 24 students were hospitalized, after one of the deadliest highway accidents in Swiss history left the front of the bus mangled, trapping some people inside. The police chief described a "scene like a war."
The bus driver, about the only person who could explain exactly what happened, died in the crash, CBS News correspondent Charlie D'Agata reports.
A Swiss prosecutor said video cameras from the tunnel captured the accident. Olivier Elsig, prosecutor for the canton of Valais, told reporters the children on the bus were wearing seat belts and no other vehicle was involved. He spoke at a news conference Wednesday in Sion, the capital of Valais.
Elsig said investigators were looking at three possible causes for the crash - a technical problem with the bus, a health problem with the driver, or human error.
He said the seatbelts wouldn't have helped much due to the severity of the crash. Experts will conduct an autopsy on the driver, he added.
Police said 21 of the dead are Belgians and seven are Dutch, while 17 of the injured are Belgian, three are Dutch, one is German, one is Polish and two others have yet to be identified.
The bus carrying 52 people, including students around age 12 from two different Belgian schools, hit a wall in the Tunnel de Geronde shortly after 9 p.m. Tuesday night on a highway near the southern town of Sierre, Switzerland, in an area of popular ski resorts.
Belgian Prime Minister Elio Di Rupo called it "an extremely sad day for all of Belgium." He arrived in Sion on Wednesday afternoon, and the Belgian government was arranging planes to fly parents and relatives of the victims to the site.
Swiss media reported the injured were taken to hospitals in Sion, Visp, Lausanne and Bern. Belga news agency cited Belgian health minister Laurette Onkelinx as saying three children remain in a coma.
Swiss President Eveline Widmer-Schlumpf also flew to Sion to pay her respects to the victims, survivors and rescue officials. The Swiss parliament held a minute of silence for the victims.
Police said the students had spent the last few days at a ski camp and were on their way back to the Belgian provinces of Brabant, Flanders and Limbourg.
While they were there, students at one school kept a blog that brimmed with enthusiasm.
"Today was totally the best," one girl wrote. "The adventurous walk was tiring but mega-cool. We won first prize for cleanest room. Tomorrow it's going to be colder. Byyyeeee!"
On day five of the vacation, a teacher posted a note meant to reassure parents back at home. "For now we do not see much homesickness," the teacher wrote. "But from the reactions of the children we gather that they miss you a little bit."
The bus was carrying students from two towns -- Lommel, east of Antwerp, and Heverlee, near Leuven. In the tunnel, it veered, hit a curb, then rammed into a concrete wall, police said. The front of the bus was heavily damaged, making it difficult for people to get out. Some had to be freed by rescuers.
"The bus hit the barrier stones on the right side of the road. It then hit the tunnel wall head on in an emergency stop space," police said in a statement. "Because of the strong impact the bus was badly damaged and several passengers were trapped in the wreckage."
"We have had a number of serious accidents in Valais but nothing like this, with so many young victims," police chief in the canton of Valais, Christian Varone said.
Initial indications are that no other vehicles were involved in the crash, which occurred in a stretch of tunnel where the speed limit was 62 miles per hour.
A government spokesman said a crisis center has been set up and an emergency number provided for families.
The Alpine city of Sierre, near Sion, the capital of Valais, is a gateway to the Val d'Anniviers tourist region and is connected to the Crans-Montana ski resort by funicular railway.
The Top Tours company, based in Aarschot, about 25 miles northwest of Brussels, was in charge of the bus that crashed. A woman who answered the phone at the company's offices declined to comment, but Belgian Transport Minister Melchior Wathelet said it has a good safety record.
"The company has an excellent reputation. The drivers had arrived (in Switzerland) the night before and rested on the day before the departure. It seems that the rules regarding driving and rest time were respected," said Wathelet. He added the bus that crashed was relatively new.
Two other buses, carrying students from schools in the Belgian towns of Beersel and Haasrode, arrived safely back in Belgium on Tuesday, apparently without having seen the accident.