From Aftenposten.no:
Stor eksplosjon i Oslo sentrum - Nyheter - Innenriks - Aftenposten.no
There has been a large explosion in central Oslo. Windows has been shattered in the VG-building and the government area of Oslo.
- all we know is that it's a kind of explosion. We're on our way there, is the short and fast report that Aftenposten.no gets from the police in Oslo, when we called a little after 4.
In a press report from the police in Oslo, it is stated:
There has been a powerful explosion in the Government area. The police received calls about this at 3:26 this afternoon.
All rescue personnel is on the site, and the police is trying to get an overview of the situation. The staff of the district has been called in.
Both windows in the government buildings and the VG-building has been blown out according to Aftenposten's reporters on the scene. They have seen several injured people.
- the police tells us that we have to leave the buildings, we must leave the buildings. There might be more than one boms, the repoerters tells.
They say that there's shards of glass everywhere, the buildings are burning.
- I see people with blood in their faces and on their hands, Aftenposten'no's reporter tells.
Our reporter passed at Torggata, and there's full chaos, people are running around in confusion. The fire alarms chime in several places. There's a smell of sulphur smoke.
The shop The Denim Gallery has had its facade blown away.
A huge smoke cloud rose several hundred meters into the air. Large parts of Oslo heard an enormous explosion, Postgirobygget was probably shaken when the explosion happened around 3:30 this afternoon.
The Vaterlandstunnel has been closed. Stortorget is being closed and Youngstorget has already been closed, most likely because the police fear more explosions.
Updating.
-------------------
Sorry about the measly translation, it went a little fast. Hope you get the meaning of the article.
-------------------
There are more as yet unconfirmed reports that there was another violent explosion at Stortingsta, just below Stortinget, according to NTB.
Photos from various norwegian and danish news sites: