Emergency services have rushed to the centre of Oslo following reports of an explosion.

Police in the Norwegian capital have confirmed that there are still explosives at the site which have not been detonated.

Armed police have now shut off the road as firefighters remain on standby to tackle any potential blazes.

Video footage has shown that a number of police helicopters were also called to the scene.

Pictures, which have circulated on social media, showed armed police putting up a cordon on Pilestredet in Oslo.

Officers have also told residents in the nearby area to stay away from their windows.

"We are working on the basis of a main theory that a hand grenade was planted," Oslo Police operations manager Øyvind Hammervold said.

In a police statement, the force added: "Residents in the area are asked to stay away from windows. Others are asked not to visit the location.

"There are explosives at the site that have not been detonated."

Despite the site being in the immediate vicinity of a university campus, no injuries have been reported in the Norwegian capital.