Powerful blast near Norwegian PM's office

A powerful explosion damaged several government buildings in central Oslo on Friday, including Norwegian Prime Minister Jens Stoltenberg's office, injuring several people.

Prime Minister Jens Stoltenberg is reportedly safe, government spokeswoman Camilla Ryste said.

At least eight people were injured in the city centre explosion, local media reports. No-one has said they were behind the attack.

Television footage from the scene showed rubble and glass from shattered windows in the streets - smoke was around some buildings. The wreckage of at least one car was in street.

Al Jazeera reports the blast blew out the windows of the building which houses the Prime Ministers office.

The cause of the blast is unknown, but a tangled wreckage of a car was spotted outside one of the buildings. The damage appeared consistent with that from car bombs. Police and fire officials however declined to comment.