GENEVA - At least 28 people, including 22 Belgian school children, were killed Tuesday night when the bus bringing them back from a skiing holiday crashed into the wall of a tunnel in Switzerland near the border with Italy, officials said Wednesday. Another 24 children were reported injured in the accident, which happened at about 9 p.m., near the town of Sierre, Belgian and Swiss officials said. The bus, transporting 52 people, mostly school children around the age 12 from Flanders, crashed in the canton of Valais, which borders Italy, police officials said. The driver, who was killed, had been at the wheel for only about 25 minutes at the start of a long overnight drive back to Belgium, police officials said. They said the bus had veered to the right, hit the curb and slammed into the wall of the tunnel. Swiss radio reports said the accident had occurred near the start of its journey at a point when the driver and his relief were well rested. The children were from two towns in Dutch-speaking Flanders, the wealthier northern region of Belgium - Lommel, about 60 miles northeast of Brussels, and Heverlee, about 20 miles east of the capital. They were aboard a modern bus that was registered in Belgium, according to Belgian radio and media reports. More than 200 police and rescue personnel were sent to the scene and helicopters were brought in to help evacuate the injured to hospitals in Bern, Lausanne and other towns in the cantons of Valais and Vaud. The Valais police commander told reporters that the tragedy was "unprecedented" and that experiences rescuers had been traumatized. There was no immediate indication of what caused the accident and both drivers were among the dead, Swiss police said. The impact of the crash was so severe that seats were torn from their mountings , said a report on La Une, a Belgian television channel, which showed images of a beige-colored vehicle with its rear section largely intact but a tangled mass of metal where the windshield and the first few rows of seats should have been.