A huge explosion went off near government headquarters in the Norwegian capital Oslo. Norway's national broadcaster NRK says at least seven people have been killed and two badly injured.

The bomb blast ripped open buildings in the heart of Norway's government quarters Friday in Oslo.

The blast blew out windows of the Prime Minister's building. It damaged the buildings of the finance and oil ministries. Glass and rubble scattered across the streets. Sirens echoed.

It was the biggest attack in western Europe since the London transport bombings in 2005. Eyewitnesses described their shock.

The normally tranquil Scandinavian nation of Norway was fitting itself into the mood for a relaxed weekend, when two attacks shocked its people as never before.

Eyewitness, said, "It is very frightening and everyone is now wondering if this was an act of terror or if it was a suicide bomber and therefore a terror action. But no one can give us an answer at the moment."

Eyewitness, said, "This is gruesome, I think I am still in shock because this is not something you expect to happen in Oslo."

Police say a bomb caused the explosion. They sealed off the scene to investigate a suspicious package.

Local media report all roads into the city center have been closed. Security officials evacuated people from the area. 

Prime Minister Jens Stoltenberg was unharmed. He described the situation as "very serious".

Jens Stoltenberg, Norwegian Prime Minister, said, "Our focus right now should be on showing solidarity and sympathy for the people who are affected. We are a small country and we are very close to each other and this is dramatic. So we will see in the hours and days ahead what is behind the incident and will know what really happened."

So far no one or group has claimed responsibility for the attack.

NATO member Norway has previously been the target of threats, over its involvement in conflicts in Afghanistan and Libya.