A bus caught fire in a town west of the Swiss capital killing at least six people and severely injuring three others, police said Tuesday.Police spokesperson, Frederic Papaux of Fribourg region, said an unspecified “voluntary act” could have caused the fire in the town of Kerzers, about 25 km west of Bern, the capital.The regional transport bus is operated by PostBus, which is affiliated with the national postal service.”After rushing to the scene, rescue teams noted that the vehicle was totally engulfed in flames,” the government said in a statement.Ambulance and helicopter teams ferried three severely injured people to the hospital, while two others were treated on site, police said.Papaux said at least six people were killed. An investigation is under way.