Four persons were killed and five injured when a five-storeyed under-construction building collapsed and fell on a hostel in Bellary, Karnataka, said the police. The mishap took place in Gandhinagar area of the city on Tuesday night. The dead included a 22-year-old student of the hostel. An injured worker rescued from the debris told the police that at least 20 people were still trapped under the debris. Rescue operations are going on.