A 13-year-old boy is reportedly among three people arrested after an explosion rang out in the centre of Oslo.
Residents were urged to stay indoors and away from their windows as police confirmed that an undetonated explosive remained at the site following the initial blast.
Pictures from the scene on Pilestredet in Oslo, Norway, show armed police have shut off the road and the surrounding area, with firefighters understood to be on standby.
Video footage also shows that several police helicopters were called to the incident, first reported by police at 7.43pm tonight.
The second device found at the site appeared to be a 'military-style' hand grenade, the police officer in charge at the scene, Brian Skotnes, told reporters at the scene.
