Police in Norway have carried out a controlled explosion on a device found on a busy commercial street in central Oslo.

One man has been arrested and is being held in custody - but authorities have refused to give any further information about the suspect.

A large area was cordoned off following the security alert on Saturday night.

Investigators said the explosive was discovered outside Groenland underground station in the centre of the city.

Heavily armoured officers swept through the surrounding area to evacuate people from bars and restaurants.

A police spokesman said the volume of the blast from the controlled explosion was, “louder than our explosives themselves would cause."

Enquiries are continuing at the scene, but detectives believe the explosive was capable of causing only a limited amount of damage.

The Groenland area is home to several popular bars and restaurants. Oslo's main police station lies less than a kilometre away from where the explosive device was found.

Witness, Malin Myrvold, who saw the police activity unfold from the fourth floor of a nearby building, said: "Every restaurant was being closed. You could see cops in heavy armour going in every store and restaurant.

"We were trying to see what was going on. The police were screaming at us to get back inside and stay where we were."

Norway was put on high alert after neighbouring Sweden suffered a truck attack in the capital Stockholm on Friday that killed four people and injured 15 others.

Additional reporting from IRN ...