Three people were seriously injured in a fierce explosion at a house in the Upper Austrian tourist town of Mondsee on Friday, according to DPA. The explosion, the cause of which was not initially known, occurred in a three-storey building in the town centre, APA news agency said. Witnesses said it was so powerful that windows in neighbouring houses were smashed. One of the injured sustained serious burns and had to be airlifted to a special hospital for burn victims in Munich. The two others were taken to hospital in the capital Voecklabruck.