A 13-year-old boy is reportedly among three people arrested after an explosion rang out in the centre of Oslo. 'More patrols have therefore been deployed in the area, and a large area has been cordoned off. 'The public is asked to stay away from the area until further notice.' 'Given that there is still an explosive device in the area, the police wish that people stay away from windows. An earlier police statement said: 'Residents in the area are asked to stay away from windows.