Oslo rocked by grenade explosion in city centre as residents told 'stay away!'

An explosion has brought central Osloto a standstill this evening with a grenade detonated by policeand one man arrested.

Norwegian police are now investigating the blast, which prompted a warning to members of the public to stay away as more explosives present were likely to be present, officers said. Drones were spotted flying above Oslo's city centre shortly after 9pm, where a controlled detonation of a grenade was carried out by police.

Residents were then alerted to the blast through a warning on their mobile phones, sent through by authorities. The message read: "There has been an explosion in the area (called) Pilestredet. Given that there is still an explosive device in the area, the police wish that people stay away from windows. As of now, we are not evacuating the area."

READ MORE: Major airport shut down as planes forced to divert amid 'large' drone incident

READ MORE: Alejandría shopping centre rocked 'by huge explosion' as cops lock down Colombian city

The detonations took place close to a university campus. No injuries have been reported at the site and the area remains taped off by police. They later found a planted hand grenade and other undetonated devices at the scene. The grenade is believed to have been left on a tram line. Oslo's Fire and Rescue Service were also notified of the incident and attended the scene to assist police.

Stunned residents told how the explosions were so loud it hurt their ears. "There was a big bang," one resident told Norwegian media outlet NRK. "We just saw someone grab a man in a hood who ran from the scene." Another witness said the area near Bislett Stadium smelt like it was burning.

It comes after drones were spotted in Oslo a day earlier. Norwegian media reported that the UAVs were flown over the Akershus Fortress, a medieval castle, with two people being arrested in connection with the incident. Up to three autonomous unmanned aerial vehicle (UAVs) were also reportedly detected in the airspace over Copenhagen Airport in Denmark as police swarmed the area and closed the airport down.

This is a breaking news story. Follow us on Google News, Flipboard, Apple News, Twitter, Facebook or visit The Mirror homepage.